Any attempt so much as to enumerate the species of nematoids infesting birds would carry me far beyond the aim and scope of this treatise. One of the commonest species is Ascaris (Heterakis) vesicularis. Many hundreds of forms have been described by Dujardin, Diesing, Molin, Krabbe, and other systematists, and it remains for some future laborer to condense the facts which are dispersed throughout a very wide-spread literature. As regards the particular species of nematoids that are either actually known or conjectured to be injurious to birds I can only find space to repeat some of the particulars which I have elsewhere recorded in respect of Sclerostoma syngamus. In 1799 a letter from Dr Wiesenthal, of Baltimore, U.S., was published in the ‘Medical and Physical Journal,’ containing an account of a parasite infesting the trachea of fowls and turkeys in America. The communication is dated May 21st, 1797, and is the first public record concerning the entozoon. Dr Wiesenthal says: “There is a disease prevalent among the gallinaceous poultry in this country, called the gapes, which destroys eight-tenths of our fowls in many parts, and takes place in the greatest degree among the young turkeys and chickens bred upon old-established farms. Chicks and poults, in a few days after they are hatched, are found frequently to open their mouths wide and gasp for breath, at the same time frequently sneezing and attempting to swallow. At first the affection is slight, but gradually becomes more and more oppressive, and it ultimately destroys. Very few recover; they languish, grow dispirited, droop, and die. It is generally known that these symptoms are occasioned by worms in the trachea. I have seen the whole [windpipe] completely filled with these worms, and have been astonished at the animals being capable of respiration under such circumstances.”

Any one who has witnessed the gapes will at once recognise the accuracy of Wiesenthal’s description; and so far as the phenomena of the disease are concerned, very little more has been added in the numerous accounts which have since appeared. On the 1st of August, 1808, the English naturalist, George Montagu, communicated to the Wernerian Society a paper entitled “Account of a species of Fasciola which infests the trachea of poultry, with a mode of cure.” Montagu does not appear to have been aware of the existence of any previous record. He gave a scientific description of the parasite, which led to its being noticed in the systematic works of Rudolphi, Dujardin, and Diesing, but the best accounts of the worm are due to Von Siebold. Sclerostoma syngamus has been found in the trachea of the turkey, domestic cock, pheasant, partridge, black stork, magpie, hooded crow, green woodpecker, starling, and swift. In July, 1860, I obtained a fowl suffering from the gapes, and operated upon it in the following manner:—A small portion of wool having been dipped in chloroform and placed in front of the nostrils the bird soon became insensible. The skin of the neck was then divided and the trachea slit up to the extent of a quarter of an inch. With a pair of common dissecting forceps, I removed seven Sclerostomata. Six of these parasites were sexually united, the odd worm being a female. After I had closed the external wound with a single thread the bird woke out of its artificial sleep, when it soon recovered its legs, and ran about the table vigorously. Moreover, in a very few minutes it devoured the contents of a saucer partly filled with bread and milk. An occasional gape was caused by an accumulation of frothy mucus within the injured trachea, but this obstruction the bird soon got rid of by shakes of the head and sneezing. The only subsequent inconvenience to the bird arose from emphysematous distension of the cellular tissue of the head and neck. This was relieved by puncture, the emphysema ceasing to form after the external wound had healed. Some months afterwards I destroyed the bird, and on dissecting the neck, a distinct cicatrix was found indicating the site of the operation on the trachea. The divided cartilaginous rings, six in number, were united only by a thin layer of connective tissue. The female worms gave an average length of 5/8″, the males scarcely exceeding 1/3″. The mouth is furnished with six prominent chitinous lips. In both sexes the surface of the body is quite smooth, but the tail of the female exhibits a tendency to fold upon itself. The lower part of the body suddenly contracts to form a short, narrow, mucronate, pointed tail. The male is usually found rigidly affixed by means of a strong, membranous, sucker-like bursa, which proceeds from the lower end of its body. In regard to the peculiar mode of union of the sexes, it becomes an interesting point to ascertain whether there be an actual incorporation of the substance of the copulatory organs during or after the act of impregnation. In my specimens none of the three pairs were organically united, and I succeeded in separating one pair very readily. Dujardin speaks of them as being soldered together, whilst the statements of Von Siebold are still more explicit. In connection with this subject the latter observer makes the following comment (‘Wiegmann’s Archiv,’ 1836, s. 106):—“The two sexes of almost all round worms are united only at the time of copulation. The male of Heteroura androphora has also the habit of remaining connected with its mate beyond the period of copulation; here, thus, there is a continuous union of the sexes without a growing together; and in Syngamus trachealis there is ultimately a lasting continuity of the sexes by means of an actual growing together.” Having confidence in Von Siebold’s statement, I concluded that the sexual union in my specimens had only recently been effected. Admitting this to have been the case, one naturally asks how the mature eggs can make their escape. Clearly, the eggs can only escape by an eventual breaking up of the body of the parent. The eggs of Sclerostoma syngamus are comparatively large, measuring 1/250″ in length. Many of the ova contained fully formed embryos, and in the centre of the lower third of the body of one of them I perceived an undulating, imperfectly formed intestinal tube. By whatever mode the young escape the shell, it is clear that they are already sufficiently developed to undertake an active migration. A change of hosts is probably necessary, but in the first instance they either enter the substance of fungi or other vegetable matters, or they bury themselves in the soil at a short distance from the surface. In view of checking the destructive influences of this parasite, the following methods have been recommended.

First. The simplest plan consists, as Dr Wiesenthal long ago pointed out, in stripping a feather from the tube to near the narrow end of the shaft, leaving only a few uninjured webs at the tip. The bird being secured, the webbed extremity of the feather is introduced into the windpipe. It is then twisted round a few times and withdrawn, when the worms are found attached. In some instances this plan succeeds entirely.

Secondly. The above method is rendered more effectual when the feather is previously steeped in some medicated solution which will destroy the worms. Mr Bartlett employs salt for this purpose, or a weak infusion of tobacco; and he informs me that the simple application of turpentine to the throat externally is sufficient to kill the worms. It should be borne in mind that the bird itself may be injuriously affected by these drugs if they are carelessly employed.

Thirdly. The treatment recommended by Mr Montagu proved successful in his hands, although the infested birds were old partridges. One of his birds had died of suffocation; but he tells us that “change of food and change of place, together with the infusion of rue and garlic, instead of plain water, to drink, and chiefly hemp-seed, independent of the green vegetables which the grass plot of the menagerie afforded, recovered the others in a very short time.”

Fourthly. The plan I employed in my experiment. This is only desirable in advanced cases, where suffocation is impending. It will afford instant relief, as the trachea may be cleared of all parasitic obstructions.

Lastly. The essential point to be observed is the total destruction of the worms. This will help to put a stop to future epizoöties. If the parasites are merely killed and thrown away carelessly, the eggs will sustain no injury. Decomposition having set in, the young embryos will sooner or later escape their shells, migrate in the soil or elsewhere, and ultimately find their way into the air-passages of birds in the same manner as their parents did before them.

In this place I must not omit to mention the remarkable circumstance, quoted in my pamphlet on the grouse disease, that Prof. Wyman, of Boston, found Eustrongyli surrounding the cerebellum in seventeen out of nineteen snake-birds or water-turkeys that had been shot in Florida. These viviparous nematodes apparently occasion their avian bearers no inconvenience. No doubt, as Wyman observes, their presence must be regarded as a normal state of things: but should they occur in excessive numbers, then we can hardly doubt the result.

As regards acanthocephalous parasites, although not so numerous as the nematodes, it is extremely probable that they play a similar rôle. Parasites which prove fatal to swine are scarcely likely to be harmless in birds. On the 18th of February, 1875, I received from Sir Joseph Hooker eleven worms for identification. Mr Charles P. Hooker, his son, subsequently informed me by letter that he had found them in a Redwing (Turdus iliacus) which he dissected in January, 1875. The worms (Echinorhynchus transversus) occupied the large intestine, probably to the number of one hundred in all. Hitherto this parasite has been found abundantly in the blackbird, thrush, and in most of the Turdidæ; but not in the redwing. It has also been obtained from the starling and red-breast. The presence of so many of these armed parasites in one small host could hardly fail to inflict severe injury on the bearer.

In concluding this section of my work I can only find space to make a few acknowledgments. Most of the rare, new, or interesting avian entozoa which I have examined and described have been received either from the Zoological Gardens, or from personal friends. In particular I may mention the collections sent to me by Mr Charles Darwin, Mr Robert Swinhoe, Mr Charles W. Devis, Dr Murie, Dr John Anderson, and Mr Spooner Hart, of Calcutta. A great many correspondents have contributed single specimens, many of which I have already incidentally acknowledged in these pages. In this place I must particularise the new species (Ascaris Cornelyi) which I described from specimens sent to Mr Sclater. This worm infests the vulturine pintado (Numida vulturina). Mr Darwin’s collection contained fine examples of Filaria horrida from the American ostrich (Rhea). When dissecting birds at the Zoological Society’s Menagerie, I obtained (in addition to the parasites already mentioned) Distoma æquale from the American owl (Strix perlata); Tænia multiformis from the night heron (Ardea nyctocorax); T. infundibuliformis from a horned pheasant (Phasianus); T. lævis and T. lanceolata and also Ascaris tribothrioides from a dusky duck (Anas obscura); Eustrongylus papillosus (fig. 75) from the larus crane (Grus antigone); Trichosoma longicolle from the horned pheasant, and T. brevicolle from the Sandwich Island goose (Bernicla Sandwichensis). This bird was also infested by Spiroptera crassicauda and Ascaris dispar. From the ring-necked pheasant (Ph. torquatus) and from the black-backed Kaleege (Euplocomus melanotus), and also from a cheer pheasant (Ph. Wallichii), I obtained abundance of Ascaris vesicularis. From the ashy-headed goose (Chloephaga poliocephala) examples of Str. tubifex and Str. nodularis. This bird also yielded a new species (Str. acuticaudatus). From a tinamou (Tinamus) I obtained the Ascaris strongylina of Rudolphi (Str. spiculatus, mihi). From amongst our British birds I have obtained Asc. depressa, Trichosoma falconum and Hemistoma spathulum, from the kite (Falco milvus). Of these three worms, the last named was also found in the long-eared owl (Strix otus), whilst the first likewise occurred in a kestrel (Falco tinnunculus) and in a honey buzzard (Pernis apivorus). I may add Filaria attenuata from a peregrine (F. peregrinus); and F. leptoptera from a sparrow hawk (Accipiter nisus). From the redshank (Totanus calidris) I obtained Tænia variabilis, and from the curlew (Numenius arcuata) T. sphærophora; and from various gulls (Larus glaucus and L. tridactylus) the Tetrabothrium cylindraceum. Also from the grey gull Echinostoma spinulosum. From the red-throated diver I procured Tetr. macrocephalum. I found this tapeworm also in the guillemot (Uria troile), together with a nematode (Ascaris spiculigera) two examples of which were lodged in the right auricle of the heart. From a capercaillie (Tetrao urogallus) I have obtained a species of Ligula, and likewise numerous examples of Trichosoma longicolle. Of necessity, this brief notice only comprises a small part of the avian entozoa contained in my collection, many of which I have not had time to describe, whilst, as regards others, I can only say that they remain in abeyance for examination and identification.

Mr Brotherston has recently recorded an interesting find (made Nov. 25th, 1874) of nematodes in the legs of the lesser grebe (Podiceps minor), and also (Feb. 27th, 1878) in the waterhen (Gallinula chloropus). Both limbs of both birds were infested. The worms of the grebe were spirally coiled amongst the muscles and tendons near the lower end of the tibia, and when unrolled measured about an inch in length. The parasites of the waterhen were similar in appearance. Not improbably these were all sexually-imperfect female examples of Filaria acuta hitherto found in the abdomen of grebes.

The British Museum contains many interesting specimens purchased from the collection of Von Siebold, but they are practically inaccessible to investigators. The entozoa in the Hunterian Collection, though few in number, are in an excellent state of preservation, and at all times accessible to visitors.

The ectozoa of birds are too numerous to be dealt with in these pages. References to recent papers by Haller, Mégnin, and Westwood will be found below. The insects infesting the domestic fowl have been alluded to in connection with the occurrence of poultry-lousiness in the horse.

Bibliography (No. 57).—(Anonymous), “On the (gape) Diseases of Fowls,” the ‘Veterinarian,’ p. 267, 1841.—(Anon., initialed “Q.”), Letter on the “Grouse Disease,” in the ‘Times,’ Sept. 5, 1874.—(Anon.), “On Grouse and Partridge Disease,” being annotations in the ‘Lancet,’ Sept. 4, 1875, pp. 360 and 361.—(Anon.), “Grouse Disease,” letter signed “R.” (probably from Lord Ravensworth), in ‘Land and Water,’ Aug. 16, 1873.—(Anon.), “Grouse Disease,” article (from “W. C.”) in the ‘Field,’ Aug. 2, 1873 (criticising my brochure.—T. S. C.).— Arlong, “Note on Tænia from the Fowl,” ‘Rec. Méd. Vét.,’ 1875.—Baird, W., “Descr. of Tænia calva from the Grouse,” in ‘Brit. Mus. Catalogue,’ p. 83.—Blavette, “Descr. of a Verminous Disease among Fowls,” ‘Veterinarian,’ p. 649, 1840.—Brotherston, A., “Parasitic Worms in Legs of Grebe (Podiceps minor) and Water-hen (Gallinula chloropus),” ‘Science Gossip’ for April, 1878, p. 88, and in ‘Proceedings of the Berwickshire Naturalists’ Club,’ vol. viii, p. 288.—Carter, B. (see Cobbold).—Chapman, H. C., “Description of a new Tapeworm from Rhea,” ‘Proceed. Phil. Acad.,’ 1876, p. 14.—Chatin, J., “Étude sur des helminthes nouveaux ou peu connus (treating of a Cyathostoma, from Anas tadorna and Sclerostoma pelecani),” ‘Annales des Sciences Naturelles,’ 1875.—Cobbold, ‘The Grouse Disease, a statement of facts tending to prove the Parasitic Origin of the Epidemic,’ London, 1874.—Idem, Letter in the ‘Field,’ Sept. 9, 1872.—Idem, “Contributions to our Knowledge of the Grouse Disease, with description of a new Species of Entozoon,” ‘Veterinarian,’ March, 1873; see also an article (by Brudenell Carter) in the ‘Times’ for Sept. 5, 1874; repr. in the ‘Veter.,’ Oct., 1874.—Idem, “Remarks on the Entozoa of the Common Fowl and of Game-birds, especially in relation to the Grouse Disease,” the ‘Field,’ Sept. 14, 1867, and ‘Brit. Assoc. Rep.,’ 1867.—Idem, “On Sclerostoma and the Disease it occasions in Birds,” ‘Linn. Soc. Proc.,’ 1861; repr. in the ‘Field,’ June 22, 1861, and in ‘Edin. Vet. Rev.,’ vol. iii, p. 439, 1861, also in Tegetmeier’s work on ‘Poultry;’ see also a comment on “Gapes,” by “Umbra,” in the ‘Field,’ June 29, 1861.—Idem, “Parasites from the Zoological Gardens,” ‘Intellectual Observer,’ 1862.—Idem., “Notes on Entozoa (species Nos. 1, 7, 9, 12),” in ‘Zool. Soc. Proc.,’ 1873–76.—Idem, ‘Linn. Soc. Trans.,’ 1858.—Idem, “On Entozoa of Birds and Fishes, collected by Mr Charles W. Devis,” ‘Zool. Soc. Proc.,’ 1865.—Idem, “Note on Entozoa in the Crested Grebe,” the ‘Field,’ March 29, 1873.—Colquhoun, W., ‘Remarks on the decrease of Grouse, and on the Grouse Disease (Gapes),’ Edinburgh, 1858; see also a notice in ‘Edin. Vet. Rev.,’ vol. i, April, 1859.—Crisp, E., “Note on Hydatids in an old Honduras Turkey,” ‘Path. Soc. Trans.,’ 1863.—Idem, “On Sclerostoma,” ‘Rep. of Path. Soc.,’ in ‘Med. Times and Gaz.,’ Oct. 26, 1876, p. 474.—Idem, “Note on Filaria in the Heart of a Peregrine Falcon,” ‘Path. Soc. Trans.,’ 1854.—Davaine, ‘Syngame de la trachée,’ p. 37, and ‘Synops.’ cxiv, in his ‘Traité.’—Devis, C. W. (see Cobbold).—Diesing, ‘Revis. der Myzelminthen,’ Abtheil. “Trémat.,” 1858.—Idem, “Tapeworm from Podiceps,” in his ‘Zwanzig Arten von Cephalocotyleen,’ Wien, 1856.—Idem, see various species in his ‘Revisionen,’ given in Bibl. No. 58.—Eames, C. J. L., “On Tapeworm in Blackbirds,” letter to the ‘Lancet,’ June 9, 1877, p. 863.—Farquharson, R., “The Grouse Disease (due to a contagious fever),” letter to the ‘Lancet,’ Sept., 1874.—Fergusson, J., “On Grouse Disease,” letter in the ‘Times,’ July 16, 1878.—Gentles, T. W., “Tapeworm in Birds,” letter to the ‘Lancet,’ Jan. 18, 1868, p. 106.—Haller, G., “Freyana und Picobia, zwei neue Milbengattungen,” in ‘Sieb. u. Köll. Zeitsch.,’ 1877, s. 181.—Johnston, D., “On the Grouse Disease,” letter in the ‘Lancet,’ Sept. 20, 1873, p. 441.—Krabbe, ‘Bidrag til Kundskab om Fuglenes Bændelorme,’ Copenhagen, 1869 (contains a summary in French, ‘Recherches sur les Ténias des Oiseaux’).—Linstow, O. von, “Euthelminthologica” (containing descriptions and notes on worms from birds, fishes, reptiles, and mollusks), ‘Archiv für Naturgeschichte,’ 1877.—Idem, “New Flukes (Dist. vitellatum and D. macrophallus) from Totanus hypoleucus, and D. cælebs from Fringilla,” Beobacht. in ‘Arch. f. Naturg.,’ 1875, s. 189–193.—Maclagan, “Note on the Grouse Disease,” ‘Proc. Roy. Soc. of Edin.,’ April 20, 1874, p. 378.—Marion, “Révis. des Némat. du Golfe de Marseilles,” ‘Compt. Rendus,’ 1875.—Mégnin, P., “On Harpirhynchus and other Mites,” in ‘Rev. f. Thierheilk.,’ Oct., 1878, s. 146.—Idem, “Mémoire sur les Cheylétides Parasites (Picobia, &c.),” ‘Journ. d’Anat. et de Physiol.,’ 1878; see also ‘Rev. f. Thierheilk.,’ Sept., 1878 et seq.—Molin, in his various monographs (quoted in Bibl. Nos. 54, 56, and elsewhere).—Montagu, G., “Account of a species of Fasciola which infests the Trachea of Poultry, with a mode of Cure,” ‘Memoirs of the Wernerian Nat. Hist. Soc.,’ vol. i, p. 194, 1811.—Perrier, ‘On Syngamus’ (brochure, Paris, 1875).—Pulteney, R., “On Ascarides discovered in Pelicanus carbo and P. cristatus,” ‘Linn. Trans.,’ vol. v, 1800, p. 24.—Röll, “Beitrag. zur Entwickelungsgeschichte der Tænien,” ‘Verh. d. Würzb. p. m. Ges.,’ Bd. iii, 1852, s. 51.—Sanderson, J. B., “On Grouse Disease,” ‘Brit. Med. Journ.,’ May 15, 1875.—Small, M., “Worms in the Eyes of Geese,” from the ‘Irish Farmer’s Gaz.,’ in the ‘Veterinarian,’ 1862, p. 19.—Tait, L., “Tapeworm in Birds,” letters to the ‘Lancet’ for Jan. 25, 1868, p. 145, and Feb. 8, 1868, p. 214; see also “Pediculus,” ibid., p. 180.—Tegetmeier, “On the Grouse Disease,” in the ‘Field,’ Sept. 12, 1874.—Thick, “Letter on the Cure of Gapes,” in ‘Land and Water,’ Aug., 1867, p. 77.—Vaughan, “The Grouse Disease,” in the ‘Field,’ Aug. 23, 1873.—Villow, A., “Sur les migrations, et les Métamorphoses des Trematodes,” ‘Comptes Rendus,’ 1875, and ‘Ann. Nat. Hist.,’ 1875 (chiefly on flukes of the sea-lark, Tringa alpina).—Idem, “Sur le syst. nerveau,” &c., ibid., 1875.—Idem, “On the Helm. Fauna of the Coast of Brittany (chiefly from birds),” ‘Ann. Nat. Hist.,’ from ‘Comp. Rend.,’ 1875, p. 1098, and from ‘Arch. de Zool. Expérim. et gén.,’ 1875.—Idem, “Sur l’appareil des Trematodes (Dist. insigne),” ‘Compt. Rend.,’ 1875.—Wedl, K., ‘Anatomische Beobachtungen ueber Trematoden,’ Wien, 1858 (contains excellent descriptions of numerous flukes, chiefly from birds).—Westwood, J. O., “New Flea on a Fowl (Sarcopsillus),” ‘Entom. Month. Mag.,’ xi, p. 246, 1875.—Wiesenthal, A., “Account of a Parasite infesting the Trachea of Fowls and Turkeys in America,” ‘Med. and Phys. Journ.,’ vol. ii, p. 204, 1799.—Wyman, “On Eustrongyli within the Cranium of Water-Turkeys,” ‘Proc. Boston Nat. Hist. Soc.,’ 1868.—Youatt, “On a Verminous Disease in Poultry” (being a letter to him), ‘Veterinarian,’ p. 648, 1840.—Zeller, “On Leucochloridium,” from ‘Zeitsch. f. wissensch. Zool.,’ 1874, s. 564, and from ‘Bibl. Univ. Bullet. Sci.,’ 1874, p. 366, in ‘Ann. Nat. Hist.,’ Feb., 1875.

Part II (Reptilia).

Much that I have advanced in respect of the parasitism of birds holds good in the case of reptiles. I cannot recapitulate. The saurians, ophidians, and chelonians are extensively infested, but in this respect the amphibian frogs, toads, and salamanders are probably the most victimised. If, on the one hand, comparatively few tapeworms have been found in reptiles, it may, on the other hand, be said that the Echinorhynchi come into prominence, causing serious injury to reptilian hosts. Serpents and chameleons are particularly liable to have their lungs infested by acanthocephalous entozoa, these organs being also attacked by pentastomes. I have received evidence of fatal epizoöty amongst chameleons from this source; and I have been requested to suggest a remedy. To prevent outbreaks of entozoal disease is one thing; to offer a radical cure when the parasites are firmly anchored within the pulmonary organs is quite another matter.

As remarked in my ‘Entozoa,’ the trematodes display a great partiality for batrachians, more than half a dozen different species of fluke being known to infest the common frog. Flukes are likewise tolerably abundant in the saurian and chelonian reptiles. I regret that I cannot find space so much as to enumerate the species. As one would naturally expect, the frog has been exhaustively anatomised and examined for entozoa, and it was this creature that supplied Leuckart and Mecznikow with the materials which led to their well-known discovery and controversy respecting the development, dimorphism, and parthenogenetic phenomena exhibited by Ascaris nigrovenosa. I cannot give the facts in detail. Female examples of the worm live in the lungs of the frog. Their young, as embryos, pass into the damp earth and mud, where they grow up into sexually-mature forms different from the parent worms found in the frog. These free adult worms, male and female, produce rhabditiform embryos which present characters of their own and attain a certain stage of growth. At this stage they are conveyed into the lungs of the frog where they arrive at sexual maturity. As there are no male worms in the frog, it is probable that the embryos of these parasitic females are agamogenetically produced by internal budding, the sexual influence of the free males being, as it were, continued onward without actual contact with the parasitic females. Amongst the interesting parasites of the frog one must also mention Amphistoma subclavatum and Polystoma intergerrimum. The former worm resides in the large intestine and the latter in the urinary bladder. The larvæ (Cercaria diplocotylea) of this amphistome reside in or upon the body of water-snails, and, like the cercarian larvæ of polystoma, they are furnished with eyes. I state this fact on the authority of Pagenstecher; and, since I cannot devote a special section to the entozoa of mollusks, I repeat, in part, the valuable results which Pagenstecher published many years back and which have a permanent value in relation to the origin of parasitic diseases resulting from flukes. In the memoir quoted below, Pagenstecher gives the following conclusions (Schlussbemerkungen):

“(a).—The eggs of the trematoda vary in respect of size, form, and color, being either furnished or not with a lid, and accordingly distinguishable. In the mature condition they contain a ciliated or a non-ciliated embryo of unequal growth, this embryo partly increasing in size even after its birth. In various conceivable ways the eggs themselves, or the embryos which have quitted their shells, arrive in and upon the bodies of mollusks, where they are consequently found. In this situation the egg opens, or the ciliated covering decays, and the contained motionless germ—which in itself offers no distinctive characters—having become free, grows into a nurse, or forms several nurses within itself.

“(b).—Whilst some of the trematodes display a highly organised nurse condition, others exhibit only a simple kind of germ-sac. Both forms, nevertheless, appear to occur in one and the same species, probably depending upon external causes.

“(c).—The organised nurses (or rediæ, as they are termed) have a mouth and a strongly marked muscular œsophagus, which is continued into a short or prolonged, single, blind intestine, or the latter may be double. The expulsion of animals developed within them I have only seen to take place through an opening at the hinder extremity. Old rediæ lose their structure. I did not observe any vascular system. Tailed trematode larvæ (Cercariæ), as well as rediæ themselves, are developed within the rediæ, this variation of nurse-contents probably depending on the season.

“(d).—No independent new germ-sacs are developed within the simple unorganised germ-sacs (sporocysts), and only such trematode larvæ as are capable of arriving at sexual maturity are furnished with special appendages.

“(e).—When the immature contents of both nurse forms (i.e. of sporocysts and rediæ) are accidentally set free, and are situated within the organs of nutrition of the living host, then they appear prepared to develop themselves anew into nurse forms; and, moreover, cercariæ whose development has not yet attained a definite stage—and even their tails also—appear to enjoy a similar capacity. Some nurses are likewise capable of multiplication by division and budding.

“(f).—Some germ-sacs have the property of developing within themselves cercaria-like larvæ—which are different from the true cercariæ—from whose body the development of a distoma may take place, while their single or double tail-like appendages in all cases develop anew into germ-sacs. To this class belong Bucephalus and Distoma duplicatum.

“(g).—All the cercaria at present known are destitute of eyes, but other forms of trematode larvæ are furnished with visual organs. Accordingly, I never found eyes in young distomata whilst they were in their last dwelling-place, but eyes are certainly present in the young forms of Polystoma and Amphistoma. The supposition that a spontaneous wandering is associated with eyes is not yet confirmed in my experience.

“(h).—As a means of distinguishing the different forms of Cercariæ, amongst other indications, their places of dwelling may be useful, because each mollusk only harbors a limited number of species. Notwithstanding, Professor Filippi is in error if he believes that every species of mollusk carries only a single armed form of cercaria. A migration of the cercaria is indispensable to its perfection.

“(i).—Many larval trematodes form cysts round themselves, probably by means of a special organ of secretion, and also by the epidermis. Their future destiny necessitates this. The sporocysts apparently fulfil towards the larvæ, which are developed within them, a similar purpose, namely, a protection against the stomachal digestion of the new host. In the pupa condition the development of the larva, which has now thrown off the tail, makes greater or less progress, according as to whether it is surrounded by nourishment or not. In particular, while in this stage, the different kinds of hooks for migratory purposes make their appearance, always, without doubt, after the shedding of the skin. Other trematodes pass through this tail-less sexually-immature stage without any cyst. I have not yet seen any larval trematode forms which had been produced in sporocysts or rediæ without appendages; they appear to occur, nevertheless.

“(k).—As the larvæ exist only in a few hosts—and most of them dwell only in one species of animal—so, also, the continued progress towards sexual maturity only succeeds in the case of certain well-defined larval organisms, but the digestion of the cysts and liberation of the larvæ may be accomplished in various animals.

“(l).—The armed Cercariæ appear to be larvæ of the spine-covered distomes of amphibia; for, as examples, the Cercaria ornata becomes transformed into Distoma clavigerum, and C. armata into Distoma endolobum; the Dist. duplicatum and Cerc. diplocotylea are, apparently, the juvenile forms of Dist. cygnoides and Amphistoma subclavatum. The Dist. echiniferum of Paludina could neither be advanced in development in the frog or duck, nor could all the other larvæ which I subjected to experiment be developed either in the green or brown frogs.

“(m).—When young trematodes arrive at the right place for their maturation, then the male generative structures develop before the female organs, and in the subsequent excess of egg production the form and structure of the animal becomes obliterated.

“(n).—The yelk-molecules surrounding the germinal vesicle are not directly transformed into an embryo.”

As regards the acantho­cephalous parasites of reptiles, I may observe that Echino­rhynchus anthuris is very common in the lesser water newt (Lisso­triton punc­tatus). In the accompanying illustration (Fig. 76) I have represented the free ovarian egg-bearing bodies, the development of the ovum, and the adult worms. For anatomical details, however, I must refer to my earlier treatise (‘Entozoa,’ p. 100 et seq.).

Amongst the species of entozoa that were found by me at the Zoological Society’s Menagerie I may mention Distoma coronarium and Ascaris lineata, from the intestines of Alligator mississippiensis; Dist. Boscii, from an American snake (Coluber); an immature nematode, from the heart of Coluber Blumenbachii; and Echinorhynchus inflexus, attached to the intestines of a snapping turtle (Chelydra serpentina). I may add that the lungs of the alligator also contained examples of Diesing’s Pentastoma oxycephalum. An Egyptian hooded snake (Naia haje), which died at the Zoological Gardens in 1859, furnished a new species of pentastome (P. multicinctum). Dr George Harley described and anatomised this worm with remarkable care. To Harley’s memoir Prof. Leuckart did ample justice in his work on the ‘Pentastoma.’ Several new species of reptilian entozoa have recently been described by Dr von Linstow; and Dr Solger has found a new trichosome (T. recurvum) beneath the skin of a young crocodile (probably Croc. acutus). For further particulars I refer to the revised descriptions and additions by Diesing, Molin, Schneider, and other systematists.

Bibliography (No. 58).—Baird, W., “Description of a new Entozoon from the Diamond Snake,” in ‘Proceed. Zool. Soc.’ for 1865, p. 58, and in ‘Ann. Nat. Hist.’ for July, 1865, p. 52.—Blanchard, “On Polystoma,” ‘Ann. des Sci. Nat.,’ 3e ser., viii, p. 331.—Canton, E., “An account of some Parasites attached to the Conjunctivæ of the Turtle’s Eyes,” ‘Quart. Journ. Micr. Sci.,’ and ‘Dublin Med. Press,’ 1861 (with remarks by myself).—Cobbold, ‘Notes,’ &c. (l. c., Bibl. No. 57), and in ‘Linn. Trans.,’ 1857.—Crisp, E., “Note on Cysticerci and Trichocephali from an Alligator,” ‘Path. Soc. Trans.,’ 1854.—Diesing, ‘Revision der Cercarieen,’ 1858; ‘Revis. der Myzelminthen,’ 1858; ‘Nachträge (u. s. w.),’ 1859; ‘Revis. der Nematoden,’ 1860; ‘Revis. d. Turbellarien,’ 1861; ‘Revis. d. Cephalocotyleen,’ 1863.—Idem, ‘Monographie d. Gatt. Amphistoma und Diplodiscus,’ and ‘Nachträge zur Monog. der Amph.,’ 1839.—Dujardin, ‘Hist. d. Helm.’ (l. c., pp. 320, 526, &c.).—Eberth, “On Myoryktes Weismanni from the Muscles of the Frog,” trans. by Busk, from ‘Siebold und Kölliker’s Zeitschrift,’ in ‘Lond. Micr. Journ.,’ Jan., 1864.—Gastaldi, ‘Cenni sopra alcuni nuovi Elmint.,’ Torino, 1854 (new flukes from frogs and salamanders).—Glüge, “On Entozoa in the Vessels of Frogs,” from ‘Comptes Rendus,’ in ‘Micr. Journ. and Struct. Rec.,’ p. 207, 1842; see Grübe and Valentin.—Grübe, “On the Entozoa of the Frog, and on the Pathology of that Batrachian,” from ‘Comptes Rendus,’ in ‘Micr. Journ. and Struct. Rec.,’ p. 246, for 1842; see also Mandl.—Harley, G., “On the Anatomy of a new Species of Pentastoma found in the Lung and Air-sac of an Egyptian Cobra,” ‘Proc. Zool. Soc.,’ June, part xxv, p. 115, 1857.—Leuckart, ‘Bau und Entwickelungsgeschichte der Pentastomen,’ Leipsig, 1860.—Linstow, ‘Enthelminth.’ (l. c., Bibl. No. 57).—Macalister, A., “On the presence of certain Secreting Organs in Nematoidea,” ‘Ann. and Mag. of Nat. Hist.’ for 1865.—Idem, “On the Anatomy of Ascaris dactyluris,” ‘Proc. Nat. Hist. Soc. of Dublin,’ vol. iv, 1865.—Mandl, “Development of Entozoa (Ascaris nigrovenosa of the frog),” from ‘Rep. of French Acad. of Sci.,’ in ‘Month. Journ. of Med. Sci.,’ vol. ii, p. 1081, 1842.—Molin, ‘Monog. del gen. Myzelminth; Mon. del gen. Physaloptera; Mon. del gen. Histiocephalus; Mon. del gen. Spiroptera;’ Wien, 1859–60.—Pagenstecher, ‘Trematodenlarven und Trematoden,’ Heidelberg, 1857.—Sibbald, J., “On the Nematoideum natricis,” ‘Path. Soc. Trans.,’ vol. viii, 1857.—Solger, “Ueber eine neue species von Trichosoma,” ‘Arch. f. Naturg.,’ 1877.—Valentin, “On Parasites in the Bladder of the Frog” (from ‘Repertorium’), in ‘Micr. Journ. and Struct. Record,’ 1842, p. 183.—Vogt, C., “On Filaria in the Vessels of the Frog,” from ‘Müller’s Archiv,’ in ‘Micr. Journ. and Struct. Rec.,’ p. 241, 1842.—Wedl, F., “Beiträge zur Lehre von den Hæmatozoen,” ‘Sitzungsb. Akad.,’ Wien, 1850 (from the blood of frogs, &c.).—Zeller, E., “Weiterer Beitrag zur Kentniss der Polystomen,” ‘Sieb. und Köll. Zeitschrift,’ 1875.

Part III (Pisces).

Swarms of entozoa infest fishes, and it is hard to say whether they are less numerous in the inhabitants of fresh water than in those of salt water. More attention has been paid to the helminths of the fishes than to the internal parasites of birds and reptiles, consequently, the number of known species must be estimated by many hundreds. In like manner a great deal has been written respecting the ectozoa of fishes. These parasites, often called fish-lice, belong chiefly to the haustellated crustaceans, and are better known by the title of Epizoa. No account of them can be afforded in this treatise, but some trifling notice of the literature of the subject will be given below.

About a hundred distinct species of fluke have been described as infesting fishes. Not many of these worms possess more than a zoological interest; nevertheless, from that point of view certain types are very curious. Most of the species dwell in the stomach and intestines, but, as more or less remarkable exceptions, I may mention Distoma seriale infesting the kidney of Salmo umbla, D. longum (Leidy) from the pharynx of Esox estor, D. polymorphum from the urinary bladder of the common pike (Esox lucius), D. obesum from the gall bladder of Salminius and other Brazilian fishes (Xiphostoma, Leporinus), D. tornatum attached to the gills of Coryphæna hippuris, D. rosaceum attached to the palate of Lota communis, and D. contortum attached to the gills of Orthagoriscus mola. Most of the forms found encysted are sexually-immature worms. To these belong D. annuligerum, found by Nordmann in cysts in the vitreous humour of the eye of the perch (Perca fluviatilis), and D. embryo from the liver and peritoneum of Acerina vulgaris. One of the largest and most remarkable of the flukes inhabiting marine fishes is the Distoma clavatum, found by Tilesius in the stomach of Pelamys, by Pohl in Thynnus, and by Bosc in Coryphæna. In the last-named fish it has been found adhering to the gills, in the liver, and in the intestines. In August, 1865, I obtained this parasite from a sword-fish (Xiphias gladius), and in the same piscine host I also found examples of four other species of helminths (Tetrarhynchus attenuatus, scolex of another tetrarhynch, Bothriocephalus plicatus, Ascaris incurva). Believing Distoma clavatum to represent several forms hitherto regarded as distinct, I append a few particulars respecting it. Five examples of this worm were obtained by me from the stomach of a sword-fish. Generally they varied in length from four lines to two inches. They differed somewhat in shape, but all had the so-called head and neck directed backwards. Below the ventral sucker the two largest specimens were distended with eggs and black pigment. All of them likewise exhibited more or less well-marked transverse rugæ, the last ring surrounding an orifice which represented the outlet of a large contractile vesicle. The eggs averaged 1/800″ in length.

When revising the entozoa of the Museum of the Royal College of Surgeons I encountered many parasites without labels attached. Amongst these were several flukes, which, though differing from each other in size and shape, appeared to be identical. One of these specimens turned out to be the particular Distoma clavatum described and figured by Professor Owen in the ‘Zoological Society’s Transactions.’ Several of the others I made out to be part of a series contributed by Mr George Bennett, who also gave specimens to the British Museum, but the College Museum stores contained yet a third group of specimens of uncertain history. The large fluke described by Prof. Owen was formerly in the collection of the Rev. Lansdown Guilding. In Dr Baird’s catalogue the specimens presented by Mr Bennett are stated to have come from the stomach of a bonito, and probably Mr Guilding’s specimens may be referred to the same “host.” Be that as it may, the specimens differ from each other in a very striking manner. In the year 1730 M. Garsin first described this worm under the generic title of Hirudinella. He says:—“Cet insecte tiré de l’estomac de la Bonita ne vécut qu’environ deux heures. Exposé à l’air il étoit languissant, et reprenoit de la vivacité dans de l’eau de mer. Il diminua sensiblement de volume pendant qu’il vivoit encore.” M. Garsin’s description is accompanied by three figures. His specimens do not appear to have exceeded 11/2″ in length. In 1774 Pallas described a trematode (Fasciola ventricosa). It measured two inches in length. All that he says regarding its source is as follows:—“Ex Amboyna missum fuit singulare hoc molluscum, quod ad aliud quam Fasciolarum genus referre non potui, in quo quasi gigas erit.” He remarks upon its pale white color, and notices particularly the soft elastic body proper, which when wounded gave out a dark matter resembling soot. This material, when examined with the microscope, appeared fresh; it was not the result of decomposition. Pallas also gives many other details, accompanied by a figure. In 1790 Menzies likewise described and figured a fluke about two inches long. He calls it Fasciola clavata:—“It is of whitish color, somewhat pellucid, discharging at its mouth a black-colored fluid, which can easily be perceived through its body. I have often found it,” he adds, “in the maws of the bonito, between the tropics in the Pacific Ocean.” Notwithstanding the similarity of description, Menzies does not appear to have recognised the identity of his worm with that described by Pallas. Prof. Owen, however, subsequently established this identity, and referred to this species as the Fasciola clavata seu ventricosa. On the other hand, the British Museum Catalogue represents Pallas’s worm as specifically distinct from that of Menzies, but as identical with the specimen described by Prof. Owen from Mr Guilding’s collection.

In 1802 Bosc described and figured a trematode under the title of Fasciola fusca. This he obtained from the intestines of a dorado. In form it differs considerably from the foregoing species. Bosc’s description runs as follows:—“Brune, la partie postérieure très-renflée, presque ovale, la partie antérieure mince, cylindrique, inégale, avec deux petits tentacules en dessous. Le suçoir de l’anus très grand.” Bosc recognised the identity of this worm with the Distoma coryphænæ of Rudolphi, and systematists generally have adopted his synonymy. In the British Museum Catalogue the Fasciola fusca and F. ventricosa of Pallas are regarded as one and the same species. The existence of two small tentacles is certainly peculiar.

In 1827 Nardo obtained two very large flukes from the stomach of a fish captured in the Gulf of Venice during the month of September. He calls the fish Prostostegus prototypus, which appears to be the same as the Luvarus imperialis of Rafinesque. One of the parasites, being five inches in length, he named Distoma gigas. His description is as follows:—“Distoma teres, rubrum, retractile; poro ventrali minimo cujus apertura magna, rotunda, ciliata; poro antico terminali, parvo; collo brevi, retrorsum divergente, extensili, apice angusto, basi lato; cauda longa, postice incrassata et in apice obtusa oscula donata.” The alleged ciliated character of the ventral sucker, was perhaps due to a wrinkled state of the lip. Apart from this character, I see no reason for supposing this parasite to be distinct from the Distoma clavatum procured by Mr Guilding, or the Fasciola ventricosa described by Pallas. The intestines of the fish harbored another parasite (D. Raynerianum). Unfortunately, Nardo gives no figure of Distoma gigas. It is the longest fluke known to science.

In the year 1835 Professor Owen communicated the memoirs already alluded to. In his paper he discussed questions relating to the structure of Distoma clavatum, and threw much light upon its anatomy, but I believe that the large “lateral cavities” described by Owen are neither more or less than the somewhat unusually distended alimentary cæca.

In 1845 Dujardin placed the worm with the true distomes, yet, at the same time, expressed grave doubts as to whether it were, in any sense, a fluke. “Ce ver,” he remarks, “n’est certainement pas un distome ni même un trématode. Si sa forme extérieure et ses deux oscules lui donnent quelque ressemblance avec les distomes, sa structure musculeuse la rapproche davantage des Gordius, et son tégument ressemble à celui des siponcles.” M. Dujardin examined the specimens preserved in the Paris Museum, and with regard to one particular example, described as “Fasciola, trouvé dans la mer de Nice,” he says, it presents “une certaine analogie avec le prétendu Distoma clavatum.” Dujardin himself was somewhat puzzled by the resemblance in question. He does not appear to have examined fresh specimens, yet he mentions the species as tolerably common in the bonito, and occasionally present in the tunny. At all events, it appears that the rightly so-called Distoma clavatum is not unfrequently taken from the ocean in the free state. In concluding my notice of this remarkable worm I can only add that after examining numerous specimens both in the fresh and preserved states, I have formed the opinion that the following specific names all refer to one and the same parasite:—Distoma clavatum, Rudolphi; D. coryphænæ, Rud.; D. gigas, Nardo; Fasciola clavata, Menzies; F. coryphænæ, Bosc; F. coryph. hippuridis and F. Scombri pelamidis, Tilesius; F. fusca, Bosc; Hirudinella marina, Garsin; H. clavata, Baird. In this list of synonyms we may probably also include Rudolphi’s Distoma tornatum.

In addition to these distomes there are numerous piscine flukes which may fairly be relegated to other genera. Thus, provisionally, I elevated Dujardin’s sub-genus Echinostoma into a separate genus; and on what I considered sufficient grounds I established several other new genera from amongst the more curious flukes that had been described as infesting fishes (Wedlia, Köllikeria). In the genus Echinostoma the oral sucker is either surrounded by a circle of little spines, or it occupies the centre of a disk, which is cleft at the ventral or anterior aspect. In the latter case the disk is either bordered both laterally and above by spines, or there are two large lobed appendages, whose margins are furnished with spines. In other respects this genus nearly corresponds with the distomes, the simple digestive tubes bifurcating immediately below the œsophageal bulb. The specimen of Ech. hispidum here drawn (Fig. 77) was taken by me from the spiral intestine of a sturgeon (1855), in which fish it occurs very abundantly. The figure represents a back view of the head and a lateral view of the body, the neck having been slightly twisted. The ventral sucker is concealed, but the transparency of the skin permits a view of the internal organs.

Another remarkable genus, established by Von Siebold, is Gasterostoma. In this genus the ventral sucker has taken the position usually assigned to the oral opening; the latter being near the centre of the body. The digestive cæca also disappear, leaving only a short stomachal cavity, which reminds one of the same viscus in imperfectly organised sporocysts or rediæ. When G. gracilescens first came under my observation I followed Rudolphi in describing it as a distome (D. gracilescens). The anatomy of the genus has been illustrated by Von Siebold; from whose observations also it may be inferred that the larvæ are various forms of Bucephali. Prof. Molin describes the water-vascular or respiratory apparatus as consisting (in G. fimbriatum) of a broad central tube, occupying the entire length of the body and opening externally at the tail.

Amongst the more remarkable fluke-types may be mentioned Van Beneden’s Nematobothrium (N. filarina), occupying the branchial cavity of Sciæna aquila, also Holostoma clavus, found by Molin in the intestines of Gadus merlucius, also Köllikeria filicollis, occupying open follicles in the branchial cavity of Brama Raii. The sexes in the last-named genus are distinct; male and female worms together occupying each cyst. The genus Monostoma is also largely represented amongst fishes. Prof. Wedl found a species (M. Wedlii) occupying follicles in the intestinal mucous membrane, and also adhering to the fin rays of Rhombus lævis. I also found a species (M. dubium) in a cyst attached to the ovary of Gasterosteus spinachii. Several species of amphistomatoid worms were found by Natterer in Brazilian fishes (Cataphractus, &c.), some of these representing distinct genera (Aspidocotylus, Notocotylus), to which I found Sonsino’s remarkable fluke (Gastrodiscus Sonsinonis, mihi) from the horse to be very closely allied. In this connection must also be mentioned Grübe and Wagener’s curious Amphiptyches urna, found attached to the branchiæ, and also in the intestines of Chimæra monstrosa.

In addition to the above families and genera of digenetic flukes infesting fishes we have the monogenetic tristomes and polystomes. As remarked in my introductory treatise, the Tristomidæ display a leech-like aspect, in consequence of which they have been placed either along with the Malacobdellidæ, or in some other allied family of the suctorial annelids. The tristomes are not strictly entozoa, yet their internal organisation conforms more to the Trematoda than to the Hirudinidæ. Thus, they support two small suckers anteriorly and one large sucker posteriorly, the body being externally smooth and devoid of annulations. The tristomes have therefore no anus. In some species the large caudal sucker is sessile, in others it is stalked or pedunculated, being in either case bordered by a membranous fold (Dujardin). All the species are hermaphroditic. They attach themselves to the gills of fishes or to the general surface, selecting especially the neighbourhood of the fins. Some species are parasitic on crustacean parasites that are themselves attached to marine fishes. In the genus Udonella the mode of development is known to be simple and direct. According to Van Beneden, the embryos are large and acquire the form and characters of their parents whilst they are still within the egg-shell. They are ready to assume an independent existence the moment they quit the shell. The eggs are oval, the chorion being prolonged into a single filamentary process or “holdfast.” Van Beneden compares a group of them to a “bouquet of vorticells.” On quitting the shell the embryonic Udonella at once attaches itself to the Caligus, and there acquires the adult condition. The Polystomidæ comprise a variety of remarkable genera. I accept this family as the equivalent of Dujardin’s first group of trematodes which he termed “Onchobothriens,” rejecting only his genus Diporpa, which is a juvenile condition of Diplozoon. In this family Van Beneden includes the genera Calceostoma and Gyrodactylus. In all the polystomes we have a more or less ramified intestine, but the reproductive organs conform to the general trematode type. All are hermaphroditic, the eggs being supplied with filamentary appendages, in some only at one pole of the shell, in others at both ends. The water-vascular system is conspicuously developed. All the species are supplied with prehensile hooks.