In Germany Dibothriocephalus latus—apart from the fact that it is undoubtedly imported from Switzerland, Russia or Italy—is particularly frequent in East Prussia amongst the inhabitants of the Courland Lagoon district, on the Baltic; it is, moreover, also found in the Province and even in the City of Königsberg. In West Prussia and Pomerania it is very much scarcer.

It is also found in Munich and in the vicinity of the Lake of Starnberg (Bollinger).

Krabbe found it in 10 per cent. of the sufferers from tapeworms in Denmark; Szydlowski found the ova of this worm in Dorpat in 10 per cent. of the fæces examined; Kruse found the worm in 6 per cent. of post-mortems; Kessler, in Petrograd, found the eggs in the fæces in 7·8 per cent.; at post-mortems he found the worms in 1·17 per cent., though Winogradoff only found it in 0·8 per cent. In Moscow, according to Baranovsky, 8·9 per cent. of the fæces examined contained the ova of Dibothriocephalus. In the interior and southern provinces of Sweden the worm, according to Lönnberg, is only found sporadically, but, on the other hand, in Angermanland about 10 per cent. of the population is affected; while again in Norbotten the majority of persons are affected, and in Haparanda the entire population (with the exception of infants) harbour this parasite. In Switzerland D. latus is very frequent in close proximity to the lakes of Bieler, Neuchatel, Morat and Geneva (according to Zaeslin 10 to 15 to 20 per cent. of the population are affected); the parasite is less frequent in districts one to four hours removed from these lakes.

Of the fish from Swiss lakes examined by Schor those from Lake Geneva were most commonly infected, and especially Lota sp. and Perea sp.

The frequency and distribution have, nevertheless, decreased perceptibly in places; at the commencement of the eighteenth century the broad tapeworm was very common in Paris, at the present date it only occurs when imported (Blanchard); in Geneva, also, according to Zschokke, it has become rarer (formerly 10 per cent., now only 1 per cent.).

The disturbances produced in man by the presence of broad tapeworms are, as a rule, very trifling; in other cases they produce partly gastric disorders and partly nervous symptoms; in a number of cases, again, they set up severe anæmia, apparently caused by toxins produced by the worms and absorbed by the host. There is no danger of auto-infection, as the larval stage lives only in fishes, not in warm-blooded animals. The case reported by Meschede (ova like those of Dibothriocephalus latus in the brain of a man who had suffered from epilepsy for six years) must be otherwise explained.

Human beings, like other hosts, can only acquire the broad tapeworm by ingesting its plerocercoids with the previously mentioned fresh-water fishes; the opportunity for such infection is afforded the more readily by the fact that not only do the lower classes not pay sufficient attention to the cooking of fish, so that all the larvæ that are present may be killed, but also in certain localities the custom exists of eating some parts of these fishes in a raw condition; even the mere handling of the usually severely infected intermediary hosts may occasionally cause infection. The plerocercoids are as well known as, but differ materially in appearance from, the cysticerci (Cysticercus cellulosæ) of pig’s flesh. In Germany the occurrence of the plerocercoids of Dibothriocephalus latus has been confirmed in the pike, miller’s thumb and perch of East Prussia, and more particularly in those taken from the Courland Lagoon.

The life of D. latus is a very long one (six to fourteen years), as is deduced from persons who have left D. latus regions after they have been infected.

According to the experiments of M. Schor, plerocercoids of D. latus placed in slowly warmed water completely lose their movement at 54° to 55° C.; they survive the death of their host for several days; they are killed by low temperatures -3° to +1° C. in two days; strong acids and salt solutions kill them at once, also high temperatures, but all the same at least ten minutes is required in boiling or frying fish in order to kill the plerocercoids with certainty.

Dibothriocephalus cordatus, R. Lkt., 1863.

Syn.: Bothriocephalus cordatus, R. Lkt.

Dibothriocephalus parvus, Stephens, 1908.

Largest gravid segments 5 by 3 mm. Uterus forms a central rosette with four to five loops on each side of median line. In a proglottid measuring 3·5 by 2·25 mm. the genital atrium is situated 0·4 to 0·5 mm. behind the anterior margin and the uterine opening the same distance behind the genital atrium. Calcareous corpuscles absent in the preserved specimens. Eggs operculated, 59·2 µ by 40·7 µ.

Distinguished from Dibothriocephalus latus—(1) by the size of gravid segments (the minimum width of gravid segments of D. latus is 10 to 12 mm., so that D. parvus is a much smaller worm); (2) quadrate segments of D. latus measure 6 by 6 mm., those of D. parvus 4 by 4 mm.; (3) by the eggs.

From D. cordatus it is distinguished by—(1) D. cordatus has only fifty immature segments, D. parvus has at least 200, possibly more; (2) mature segments of D. cordatus measure 7 to 8 mm., maximum width of D. parvus is 5 mm.; (3) quadrate segments of D. cordatus measure 5 to 6 mm.; (4) D. cordatus has six to eight uterine loops; (5) D. cordatus measures 75 µ to 80 µ by 50 µ.

Habitat.—Intestine of man (Syrian, in Tasmania).

Genus. Diplogonoporus, Lönnbrg., 1892.

Syn.: Krabbea, R. Blanch., 1894.

The scolex is short and has powerful suctorial grooves; no neck; the proglottids are short and broad; there are two sets of genital organs side by side in each segment, which in all essentials resemble the single one of Dibothriocephalus.

Parasitic in whales and seals, occasionally in man.

Diplogonoporus grandis, R. Blanch., 1894.

Syn.: Bothriocephalus sp., Ijima et Kurimoto, 1894; Krabbea grandis, R. Blanch.

Scolex unknown; chain of proglottids over 10 m. in length, 1·5 mm. broad anteriorly, 25 mm. broad posteriorly. The proglottids are very short (0·45 mm.), but 14 to 16 mm. broad. On either side to the right and left of the worm, along the entire ventral surface, there is a longitudinal groove; these grooves are nearer to each other than to the lateral margin; in them lie the genital pores, and they are in the same sequence as in Dibothriocephalus; corresponding to the scanty length (0·45 mm.) of the proglottids, the ovary is only developed transversely; the uterus only makes a few loops. Eggs (fig. 195) thick shelled, brown, 63 µ by 48 µ to 50 µ. This parasite has hitherto been observed twice in Japanese. Similar species are known in Cetacea and seals.

These plerocercoids were discovered in 1882 by P. Manson during the post-mortem on a Chinaman who had died in Amoy, twelve specimens being found beneath the peritoneum and one free in the abdominal cavity. Cobbold described them as Ligula mansoni, and Leuckart, who contemporaneously reported a case in Japan, termed them Bothriocephalus liguloides. Ijima and Murata reported eight further cases, and Miyake records nine further cases, seven of which are recorded in Japanese literature.

The plerocercoid, which hitherto alone is known to us, attains a length of 30 cm. and a breadth of 3 to 6 to 12 mm. The ribbon-shaped body is wrinkled, the lateral borders are often somewhat thickened, so that the transverse section has the form of a biscuit; the anterior end is usually wider and has the head provided with two weak suctorial grooves, either retracted or protracted.

The parasite makes migrations within the body, and thus may reach the urinary passages; then it is either evacuated with the urine or has to be removed from the urethra; not rarely it causes non-inflammatory tumours on various parts of the skin, which are at times painful and at times vary in size.

Nothing is known of its development and origin.

Sparganum proliferum, Ijima, 1905.

Syn.: Plerocercoides prolifer, Ijima, 1905; Sparganum prolifer, Verdun, Manson, 1907.

Each capsule, as a rule, contains one worm, but as many as seven may occur. The skin of areas that have been long infected is swollen and indurated or adherent, giving a somewhat elephantoid appearance. The subcutaneous tissue is thick and filled with slimy fluid or in other parts sclerosed.

The simplest forms are thread-like bodies, flat or round, 3 mm. long and 0·3 mm. in diameter, but they may be 12 mm. long by 2·5 mm. broad. The narrow end is the head, which in life invaginates and evaginates, but there is no indication of any suckers, except an inconstant terminal depression. In addition to these simple forms the most complicated and irregular forms occur, due to the formation of buds (heads) at various parts. The detachment and growth of a head account for the presence of more than one worm in a cyst. The irregularity in form is also increased by the presence in the subcuticular tissue of the worm of reserve food bodies. These bodies are supposed to be of this nature and are spherical, 100 µ to 300 µ in diameter, but also much elongated.

Calcareous bodies in the Japanese worms were 7·5 µ to 12 µ; in the Florida worms 8·8 µ to 17·6 µ.

This worm measures 15 to 35 cm. in length and 1·5 to 3 mm. in breadth. The scolex is small, rhomboidal, and has a club-shaped rostellum on which there are, in three to four rings, forty-eight to sixty hooks resembling rose thorns, the size of those in the foremost being 11 µ to 15 µ and those in the hindmost ring 6 µ. The neck is very short, the most anterior segments broad and short, the middle as long as they are broad; the mature segments are longer than wide (6 to 7 mm. by 2 to 3 mm.), fairly thick, are frequently of a reddish colour, and when cast off resemble cucumber seeds. The genital pores lie symmetrically at the lateral margins; the roundish egg sacs, arising from the uterine reticulum, contain eight to fifteen eggs embedded in a reddish cement substance (in life). The eggs are globular (43 µ to 50 µ,); the embryonal shell (embryophore) is thin, the oncosphere measures 32 µ to 36 µ. Surrounding the embryophore is an albuminous coating, and outside this the thin vitelline envelope (fig. 218).

The corresponding larval form (cysticercoid) lives in the louse of the dog (Trichodectes canis), a fact that was first established by Melnikow and Leuckart; according to Grassi and Rovelli, as well as Sonsino, it also lives in the flea of the dog (Ctenocephalus canis) and in the flea of man (Pulex irritans), but not in its larva. The adult segments, which also leave the rectum of dogs and cats spontaneously, creep about around the anus and get into the hair, and are thus partly dried and disintegrated. Part of the segments, or the oncospheres released by disintegration, are then taken up by lice and fleas, within which they develop into larvæ (cysticercoids). Dogs and cats are thus infected by their own skin parasites, which they bite and swallow whilst gnawing at their fur. The infection of human beings must occur in an analogous manner, by transmission of the cysticercoids present on the lips or tongue of dogs when the latter lick them, or it may be that the vermin of cats and dogs harbouring cysticercoids are accidentally and directly swallowed by human beings.

Family. Hymenolepididæ, Railliet and Henry, 1909.

Genus. Hymenolepis,282 Weinland, 1858.

This species was discovered by Bilharz in Cairo in 1851; it was found by him in great numbers in the intestine of a boy who had died of meningitis. For several years this was the only case, until 1885, since when numerous cases have come to light. Spooner (1873) even reported a case from North America, which may, however, have related to Hymenolepis diminuta. In Europe the worm is particularly frequent in Sicily, but it has also been repeatedly observed in North Italy; it has, moreover, been reported from Russia, Servia, England, France, Germany, North and South America, the Philippines, Siam and Japan, in all over 100 cases. Notwithstanding its small size this worm causes considerable disorders in its hosts—mostly children—as it sets up loss of appetite, diarrhœa, various nervous disturbances, and even epilepsy; all these symptoms, however, disappear after the expulsion of the parasites, which are generally present in large numbers.

The development as well as the manner of infection is still unknown; Grassi is of opinion that Hymenolepis nana is indeed merely a variety of Hymenolepis murina, Duj., which lives in rats. According to Grassi direct development takes place with omission of the intermediate host, but with the retention of the larval stage; that is to say, rats infect themselves directly with Hymenolepis murina, by ingesting the mature segments or oncospheres of this species, from which subsequently the small larvæ originate in the intestinal wall (fig. 225); when fully developed they fall into the intestinal lumen and become tapeworms. The identity of the two forms has nevertheless been disputed (Moniez, R. Blanchard, v. Linstow), though their near relationship cannot be denied. Grassi gave mature segments of Hymenolepis murina to six persons, but only one person evacuated a tapeworm. This, however, proves nothing in a district where Hymenolepis nana frequently occurs in man; it was, moreover, not possible to infect rats with segments of Hymenolepis nana (of man). Accordingly this form may represent an independent species, which, however, like Hymenolepis murina, also omits an intermediate host.

Hymenolepis diminuta, Rud., 1819.

Syn.: Tænia diminuta, Rud., 1819; Tænia leptocephala, Crepl., 1825; Tænia flavopunctata, Weinld., 1858; Tænia varesina, E. Parona, 1884; Tænia minima, Grassi, 1886.

This species measures 20 to 60 cm. in length, and up to 3·5 mm. in breadth; there are from 600 to 1,000 segments. The head is very small (0·2 to 0·5 mm.), it is club-shaped and has a rudimentary unarmed rostellum; the neck is short; the mature segments are 3·5 mm. in breadth, 0·66 mm. in length; the eggs are round or oval. The outer egg-shell is yellowish and thickened, with indistinct radial stripes; the inner embryonal shell (embryophore) double, thin; the outer layer is somewhat pointed at the poles; oncosphere 28 µ by 36 µ. Between the inner and outer shells is a middle granular layer.

Hymenolepis diminuta lives in the intestine of rats—Mus decumanus (the sewer rat), Mus rattus (the black rat), and Mus alexandrinus, rarely in mice; it is occasionally also found in human beings.

Weinland described it from specimens collected by Dr. E. Palmer in 1842, in Boston, from a child aged 19 months, as T. flavopunctata. A second case relating to a three year old child, from Philadelphia, was only reported in 1889 by Leidy; a third case was simultaneously reported of a two year old girl in Varese (T. varesina); and Grassi described another case relating to a twelve year old girl from Catania (Sicily). Sonsino and Previtera reported the same species in Italy, Zschokke in France, Lutz and Magalhães in South America, and Packard in North America: a total of twelve cases, five from America, the rest from Europe (Ransom).

Nicoll and Minchin283 found in the body cavity of 4 per cent. of rat fleas (Ceratophyllus fasciatus) the cysticercoid of Hymenolepis diminuta. That it belonged to this species was shown by its unarmed rostellum and by feeding; 340 fleas were fed to white rats and fourteen worms obtained, i.e., about 4 per cent., thus corresponding to the infection of the fleas. The development in the flea probably begins in the pupal stage, the eggs being ingested by the older flea larvæ. The larva is 0·31 by 0·25 mm.; tail 0·8 mm., scolex 0·075 by 0·09 mm., suckers, 0·055 mm. in diameter. Microscopically it shows—(1) externally a radially striated layer resembling cuticle, (2) a layer of columnar cells, (3) parenchymatous layer continuous with the tail, (4) fibrous layer around the small caudal vesicle, then the parenchymatous scolex at the bottom of the secondary cavity.

Nicoll and Minchin (loc. cit.) found a cysticercoid284 in the rat flea Ceratophyllus fasciatus which was probably that of Hymenolepis murina. Body 0·16 mm., tail 0·19 mm., scolex 0·096 mm. in diameter. Rostellum has twenty-three spines in a single row. Length 0·017 mm., handle 0·01 mm., guard 0·007 mm., prong 0·007 mm. Sucker 0·042 mm. Although this cycle, then, for H. murina also exists, it is not probable that rats (or man in the case of H. nana if this be considered distinct) infect themselves in this way, as they hardly ingest all the necessary fleas to account for the massive infection which frequently exists in rats (and man), so that Grassi’s cycle holds good as the predominant method. Xenopsylla cheopis has also been found by Johnston to harbour both cysticercoids in Australia.

The parasite measures 30 to 130 mm. in length and 5 to 18 mm. in breadth; the head is globular and very small; the rostellum is cylindrical, with a circlet composed of eight hooks (31 µ to 35 µ in length). The neck is very short. The short segments increase gradually and equally in breadth, but only a little in length; the female glands lie on the side opposite to that on which the genital pore is situated; the three elliptical testes are on the same side as the pores; the cirrus is armed and slender. The eggs have three envelopes and are oval (50 µ by 35 µ), the external envelope is thin, the middle intermediate layer or envelope is not so marked as in H. diminuta, and the internal one is very thin and sometimes has polar papillæ, as in Hymenolepis diminuta and H. nana.

This worm measures 25 to 30 cm. in length; the head has four large round suckers; the rostellum has ninety hooks (18 µ in length); there are 500 to 700 segments, of which the last 100 are filled with eggs and form half of the entire worm. The segments, when mature, measure 2 mm. in length by 1·4 mm. in breadth; genital pores unilateral; about fifty testes; the uterus consists of a number of loops, which at each side are rolled up into an almost spherical ball; when filled with eggs the convolutions unwind, permeate the segment and then lose their wall; the eggs lying free in the parenchyma become finally surrounded, one, or several together, by proliferating parenchymatous cells; this is how the 300 to 400 egg masses, taking up the entire mature segment, are formed. The globular oncosphere (8 µ) is surrounded by two perfectly transparent shells, the outer of which terminates in two pointed processes.

Davainea madagascariensis has hitherto been found in man only (eight times). Davaine described this species from fragments sent to him from Mayotta (Comoro Islands), which were found in two Creole children. Chevreau observed four cases in Port Louis (Mauritius), likewise in children; Leuckart received the first perfect specimen—it was obtained from a three year old boy, the son of a Danish captain, in Bangkok; Daniels, at the post-mortem of an adult native of George Town, Guiana, found two specimens (Tænia demerariensis); and finally Blanchard describes another perfect specimen which was in Davaine’s collection of helminthes in Paris, and which was obtained from a little girl 3 years old, of Nossi-Bé (Madagascar). The intermediate host is unknown.

Davainea (?) asiatica, v. Linst., 1901.

Syn.: Tænia asiatica, v. Linstow.

There exists only one headless specimen of this species, which is not quite adult, and which is preserved in the Zoological Museum of the Imperial Academy of Science in Petrograd. It came from a human being and was found by Anger in Aschabad (Asiatic Russia, near the northern frontier of Persia). The specimen measures 298 mm. in length. The breadth anteriorly is only 0·16 mm., the posterior part measures 1·78 mm. across. The number of segments is about 750. The genital pores are unilateral; the testes are globular and lie in a dorsal and ventral layer in the medullary layer; the cirrus pouch is pyriform, 0·079 mm. in length and 0·049 mm. in breadth; the female glands lie in the fore-part of the segments, the ovary reaching to the excretory vessels; the vitellarium is small and round. The vagina has a large fusiform receptaculum seminis; the uterus breaks up into sixty to seventy large, irregularly polyhedric eggsacs.

Family. Tæniidæ, Ludwig, 1886.

Genus. Tænia, L., 1758.286

Tænia solium, L., p. p., 1767.

Syn.: Tænia cucurbitina, Pall., 1781; Tænia pellucida, Goeze, 1782; Tænia vulgaris, Werner, 1782; Tænia dentata, Gmel., 1790; Halysis solium, Zeder, 1800; Tænia humana armata, Brera, 1802; Tænia (Cystotænia) solium, Lkt., 1862.

The average length of the entire tapeworm is about 2 to 3 m., but may be even more; the head is globular, 0·6 to 0·8 to 1·0 mm. in diameter. The rostellum is short with a double circlet of hooks, twenty-two to thirty-two in number, usually twenty-six to twenty-eight; large and small hooks alternate regularly; the length of the large hooks is 0·16 to 0·18 mm., of the small ones 0·11 to 0·14 mm. The rostellum is sometimes pigmented. The suckers are hemispherical, 0·4 to 0·5 mm. in diameter. The neck is fairly thin and long (5 to 10 mm.). The proglottids, the number of which averages from 800 to 900, increase in size very gradually; at about 1 m. behind the head they are square and have the genitalia fully developed. Segments sufficiently mature for detachment measure 10 to 12 mm. in length by 5 to 6 mm. in breadth. The genital pores alternate fairly evenly at the lateral margin a little behind the middle of each segment. The fully developed uterus consists of a median trunk, with seven to ten lateral branches at either side, some of which are again ramified. The eggs are oval, the egg-shell very thin and delicate; the embryonal shell (embryophore) is thick, with radial stripes; it is of a pale yellowish colour, globular, and measures 31 µ to 36 µ in diameter; the oncospheres, with six hooks, are likewise globular, and measure 20 µ in diameter (fig. 238).