Velum penis.—In the locusts (Acrydiidæ) the penis is concealed by a convex plate, flap, or hood, free anteriorly and attached posteriorly and on the sides to the ridge forming the upper edge of the tenth sternite. When about to unite sexually, the tip of the abdomen is depressed, the hood is drawn backward, uncovering the chitinous penis.

The suranal plate.—This is a triangular, often thick, solid plate or area, the remnant of the tergum of the last, usually tenth, segment of the abdomen, the supra-anal or suranal plate, or anal operculum (lamina supra-analis) of Haase. In most lepidopterous larvæ this plate is well marked; in those of the Platypteridæ it is remarkably elongated, forming an approach to a flagellum-like terrifying appendage, and in that of Aglia tau it forms a long, prominent, sharp spine. In the cockroach, both Cholodkowsky and Haase maintain that the tenth abdominal segment is suppressed in the female, the tergal portion being fused with the suranal plate (the latter in this case, as we understand it, being the remnant of the eleventh segment of the embryo). As to the nature of the middle jointed caudal appendage in Thysanura and May-flies Heymons has satisfactorily shown that it is a hypertrophied portion of the suranal plate, being in Lepisma but a filamental elongation of the small eleventh abdominal tergite.

At the base of the suranal plate of locusts (Acrydiidæ) is the suranal fork or suranal furcula (furcula supra-analis, as we have called it) (Fig. 88, 89, f).

The podical plates or paranal lobes.—In the cockroach and other insects, also in the nymphs of Odonata, the anus is bounded on each side by a more or less triangular plate, the two valves being noticeable in lepidopterous larvæ. They are the valvulæ of Burmeister, and podical plates of Huxley, who also regarded them as the tergites of an eleventh abdominal segment;^[38] and the subanal laminæ of Heymons. They are wanting in Ephemeridæ.

The infra-anal lobe.—Our attention was first called to this lobe or flap, while examining some geometrid larvæ. It is a thick, conical, fleshy lobe, often ending in a hard, chitinous point, and situated directly beneath the vent. Its use is evidently to aid in tossing the pellets of excrement away so as to prevent their contact with the body. The end may be sharp and hard or bear a bristle. Whether this lobe is the modified ventral plate of the ninth urite, we will not undertake at present to say.

The egg-guide.—In the Acrydiidæ the external opening of the oviduct is bounded on the ventral side by a movable, triangular, acute flap, the egg-guide (Fig. 88, B, eg). Whether this occurs in other orders needs to be ascertained.

LITERATURE ON THE ABDOMEN AND ITS APPENDAGES

a. General (including the cerci, stili, etc.)

Cornelius, C. Beiträge zur naheren Kenntnis von Palingenia longicauda. (Programm d. Real- u. Gewerbeschule zu Elberfeld, 1848, pp. 1–38, 4 Taf.)

Schiödte, J. G. Bemerkungen über Myrmecophilen. Ueber den Bau des hinterleibes bei einigen Käfergattungen. (Germar’s Zeits. f. Ent., 1844.)

—— De metamorphosi Eleutheratorum observationes. (Naturhist. Tidsskr. i-xiii, 1861–1883.)

Meinert, F. Anatomia Forficularum. Anatomisk undersogelse af de Danske Orentviste, i. (Naturhist. Tidsskr. 3 raekke, ii, 1863, pp. 427–482, 1 Pl.)

—— Om dobbelte Saedgange hos insecter. (Naturhist. Tidsskrift, 3 raekke, v, 1868.)

Tullberg, Tycho. Sveriges Podurider. (Svenska Vetensk.-Akad. Handl., 1872, x, Nr. 10, 12 Pls.)

Davis, H. Notes on the pygidia and cerci of insects. (Journ. R. Micr. Soc., 1879, ii.)

Westhoff, F. Ueber den Bau des Hypopygiums der Gattung Tipula Meig. (Münster, 1882, pp. 1–62, 6 Taf.)

Saunders, Edward. Further notes on the terminal segments of aculeate Hymenoptera. (Trans. Entom. Soc. London, 1884, pp. 251–267, 1 Pl.)

Palmén, J. A. Ueber paarige Ausführungsgange der Geschlechtsorgane bei Insekten. (Helsingfors, 1884, 5 Taf.)

Haase, E. Die Abdominalanhänge der Insekten mit Berücksichtigung der Myriopoden. (Morpholog. Jahrbuch, 1889, xv, pp. 331–435, 2 Taf.)

—— Abdominalanhänge bei Hexapoden. (Sitzungsber. d. Gesellsch. naturforsch. Freunde, 1889, pp. 19–29.)

Wheeler, William M. On the appendages of the first abdominal segment of embryo insects. (Trans. Wis. Acad. Sc., viii, 1890, pp. 87–140, 3 Pls.)

Janet, Charles. Études sur les fourmis, 5^e note, sur la morphologie du squelette des segments post-thoraciques chez les Myrmicides. (Mém. Soc. Acad, de l’Oise, xv, pp. 591–611, Figs. 1–5, 1894.)

Heymons, Richard. Die Segmentirung des Insektenkörpers. (Anh. Abh. Akad. Berlin, Phys. Abh., pp. 39, Taf., 1895. See also Die Embryonalent, von Dermapteren und Orthopteren, under Embryology.)

—— Grundzüge der Entwicklung und des Körperbaues von Odonaten und Ephemeriden. (Abhandl. k. Preuss. Akad. d. Wissens. Berlin, 1896, 2 Taf., pp. 1–66.)

—— Zur Morphologie der Abdominalanhänge bei den Insecten. (Morphol. Jahrb., iv, 1896, pp. 178–203, 2 Taf.)

Peytoureau, S. A. Contribution à l’étude de la morphologie de l’armure génital des insectes. (Bordeaux, 1895, pp. 248, 22 Pls., 43 Figs. in text.)

Verhoeff, C. Cerci und styli der Tracheaten. (Ent. Nachr., xxi, pp. 166–168, 1895.)

Also the writings of Oudemans, Packard, etc.

b. The ovipositor

Lacaze-Duthiers, Henri. Recherches sur l’armure génitale femelle des insectes. (Ann. d. sc. natur., 1849, xii, pp. 353–374, 1 Pl.; 1850, xiv, pp. 17–52, 1 Pl. (Hyménoptères); 1852, xvii, pp. 206–251, 1 Pl. (Orthoptères); 1853, xix, pp. 25–88, 4 Pl. (Neuroptères, Thysanures, Coléoptères, Diptères); pp. 203–237 (Lépidoptères, Aphaniptères en general. Also separate.))

Sollmann, A. Der Bienenstachel. (Zeitschr. f. Wissens. Zool., xiii, 1863, pp. 528–540, 1 Taf.)

Fengger, H. Anatomie und Physiologie des Giftapparates bei den Hymenopteren. (Archiv f. Naturgesch., 1863, pp. 139–178, 1 Taf.)

Eaton, A. E. Remarks upon the homologies of the ovipositor. (Trans. Ent. Soc. London, 1868, pp. 141–144.)

Packard, A. S. On the structure of the ovipositor and homologous parts in the male insects. (Proc. Boston Soc. Nat. Hist., xi, 1868, pp. 393–399, Figs. 1–11.)

Lambrecht, A. Samtliche Teile des Stechapparates in Bienenkörper und ihre Verwendung zu technischen und vitalen Zwecken. (Bienemwirtsch. Centralbl., 7 Jahrg., 1871, pp. 5–11.)

Kraepelin, K. Untersuchungen über den Bau, Mechanismus und die Entwicklung des Stachels der bienenartigen Tiere. (Zeitschr. f. wiss. Zoologie, xxiii, 1873.)

Dewitz, H. Vergleichende Untersuchungen über Bau und Entwicklung des Stachels der Honigbiene und der Legescheide der grünen Heuschrecke. (Königsberg, 1874.)

—— Ueber Bau und Entwicklung des Stachels und der Legescheide einiger Hymenopteren und der grünen Heuschrecke. (Zeitschr. f. wissen. Zoologie, xxv, 1874, pp. 174–200, 2 Taf.)

—— Ueber Bau und Entwicklung des Stachels der Ameisen. (Zeitschr. f. wiss. Zoologie, 1877, xxviii, pp. 527–556, 1 Taf.)

Adler, H. Legeapparat und Eierlegen der Gallwespen. (Deutsche Entom. Zeitschr., 1877, xxi Jahrg., pp. 305–332, 1 Taf.)

Cholodkowsky, N. Ueber den Hummelstachel und seine Bedeutung für die Systematik. (Zool. Anzeiger, vii, 1884, pp. 312–316.)

Ihering, H. von. Der Stachel der Meliponen. (Ent. Nachr., 1886, xii, Jahrg., pp. 177–188, 1 Taf.)

Meinert, F. Bidrag til de danske Myrers Naturhistorie. (Kjöbenhavn, 1890, 68 s.u. Danske Vidensk. Selsk. Skrifter, 5 Raek, v, 3 Pls.)

Beyer, O. W. Der Giftapparat von Formica rufa ein reduziertes Organ. (Jena. Zeitschr. Naturw., 1890, xxv, pp. 26–112, 2 Taf.)

Carlet, G. Mémoire sur le venin et l’aiguillon de l’abeille. (Ann. d. sc. nat. Zool., 7 sér., ix, 1890, pp. 1–17, 1 Pl.)

Künckel d’Herculais, J. Méchanisme physiologique de la ponte chez les insectes orthoptères de la famille des Acridides.—Rôle de l’air comme agent mécanique et fonctions multiples de l’armure génitale. (Compt. Rend., cxix, pp. 244–247, 1894.)

Also the writings of Verhoeff, Heymons.

c. The external genital armature

Klug, Johann C. F. Versuch einer Berichtigung der Fabriciusschen Gattungen Scolia u. Tiphia. (Ueber u. Mohr Beiträge zur Naturkunde, i, pp. 8–40, 1805, 1 Taf.)

Audouin, J. V., and Lachat. Observations sur les organes copulateurs males des Bourdons. (Annal. général, d. sc. phys., 1821, viii, pp. 285–289.)

Audouin, J. V. Lettre sur la génération des insectes. (Ann. des sc. nat., sér. 1, ii, 1824.)

Suckow, F. W. L. Geschlechtsorgane der Insekten. (Heusinger, Zeitschr. organ. Physik., 1828, ii, pp. 231–264, 1 Taf.)

Rathke, H. De Libellularum partibus genitalibus. Regiomonti, 1832, pp. 6 + 38, 3 Pls.

Siebold, C. Th. E. von. Ueber die Fortpflanzungsweise der Libellulinen. (Germar’s Zeitschr. f. Ent., 1840, ii, pp. 421–438.)

Selys-Longchamps, E. de. Monographie des Libellulidees d’Europe. 4 Pls., 1840.

Bassi, C. A. Studi sulle funzioni degli organi genitali degl’ insetti da lui osservati piu specialmente nella Bombyx mori. (Atti della 5 Riun. d. Scienz. Ital. Lucca, 1844, pp. 39–94.)

Stein, F. Vergleichende Anatomie und Physiologie der Insekten, i. Die weiblich. Geschlechtsorgane der Käfer. Berlin, 1847, 9 Taf.

Ormancey, P. Recherches sur l’étui penial considéré comme limite de l’espèce dans les coléoptères. (Ann. sc. nat., 1849, 3 sér., Zool., xii, pp. 227–242.)

Roussel, C. Recherches sur les organes génitaux des insectes coléoptères de la famille des Scarabéides. (Compt. rend. Acad. d. sc. Paris, 1860, l, pp. 158–161.)

MacLachlan, R. A monographic revision and synopsis of the Trichoptera of the European fauna. London, 1874–80, 59 Pls.

—— On the sexual apparatus of the male Acentropus. (Trans. Ent. Soc. London, 1872, pp. 157–162.)

Thomson, C. G. Nagra anmarkningar ofver arterna af slagtet Carabus. (Thomson’s Opuscula Entomologica, vii, 1857, pp. 615–729, 1 Pl.)

Dufour, L. Sur l’appareil génital male du Coræbus bifasciatus. (Thomson, Archiv ent., 1857, i, pp. 378–381.)

White, F. Buchanan. On the male genital armature in the Rhopalocera. (Trans. Linn. Soc., ser. 1, Zool., i, pp. 357–369, 1876, 3 Pls.)

Graber, V. Die Aehnlichkeit im Baue der ausseren weiblichen Geschlechtsorgane bei den Lokustiden und Akridiern auf Grund ihrer Entwicklungsgeschichte. (Sitzber. k. Akad. d. Wissensch. Wien., 1870, lxi, pp. 1–20, 1 Taf.)

Scudder, Samuel H., and Edward Burgess. On asymmetry in the appendages of hexapod insects, especially as illustrated in the lepidopterous genus Nisoniades. (Proc. Boston Soc. Nat. Hist., 1871, xiii, pp. 282–306.)

Chadima, J. Ueber die Homologie zwischen den männlichen und weiblichen ausseren Sexualorganen der Orthoptera Saltatoria Latr. (Mitteil. d. naturwiss. Vereins f. Steiermark, 1872, pp. 25–33, 1 Taf.)

Hagens, von. Ueber die Genitalien der männlichen Bienen, besonders der Gattung Sphecodes. (Berlin Ent. Zeitschr., 1874, pp. 25–43.)

—— Ueber die männlichen Genitalien der Bienengattung Sphecodes. (Deutschen Entom. Zeitschr., 1882, pp. 209–228, 2 Taf.)

Lindenman, C. Vergleichend-anatomische Untersuchung ueber das männliche Begattungsglied der Borkenkäfer. (Bull. Soc. Imp. d. Natural. Moscou, 1875–77.)

Forel, A. Der Giftapparat und die Analdrüsen der Ameisen. (Zeitschr. f. wiss. Zoologie, xxx, suppl., 1878.)

Kraatz, G. Ueber die Wichtigkeit der Untersuchung des männlichen Begattungsgliedes der Käfer für die Systematik und Artunterscheidung. (Deutschen Entom. Zeitschr., 1881, xxv, pp. 113–126.)

—— Ueber das männliche Begattungsglied der europaischen Cetoniiden und seine Verwendbarkeit für deren scharfe spezifische Unterscheidung. (Ibid., pp. 129–149.)

Gosse, Ph. H. On the clasping-organs ancillary to generation in certain groups of the Lepidoptera. (Trans. Linn. Soc., 1882, Ser. 2, Zool., ii, pp. 265–345, 8 Pls.)

—— The prehensors of male butterflies of the genera Ornithoptera and Papilio. (Proc. Roy. Soc. London, 1881, xxxiii, pp. 23–27.)

Radoszkowski, O. Revision des armures copulatrices des males du genre Bombus. (Bull. Soc. Natur. Moscou, 1884, xlix, pp. 51–92, 4 Pls.)

—— Revision des armures copulatrices des males de la tribu Philérémides. (Ibid., 1885, lxi, pp. 359–370, 2 Pls.)

—— Revision des armures copulatrices des males de la famille des Mutillidæ. (Horæ Soc. Ent. Ross., 1885, xix, pp. 3–49, 9 Pls.)

—— Revision des armures copulatrices des males de la tribu des Chrysides. (Horæ Soc. Ent. Ross, xxiii, 1890, pp. 3–40, 6 Pls.)

Hofmann, O. Beiträge zur Kenntnis der Butaliden. (Stett. Ent. Zeit., 1888, pp. 335–347, 1 Taf.)

Driedzichi, H. Revue des espèces européennes du genre Phronia Winn. (Horæ Soc. Ent. Ross., 1889, xxiii, pp. 404–532, 10 Pls.)

Sharp, David. On the structure of the terminal segment in some male Hemiptera. (Trans. Ent. Soc. London, 1890, pp. 399–427, 3 Pls.)

Escherich, K. Die biologische bedeutung der Genitalanhänge der Insekten. (Verhandl. d. zool. bot. Ges. Wien., 1892.)

—— Anatomische Studien über das männliche Genitalsystem der Coleopteren. (Zeits. f. wissens. Zool., lvii, pp. 620–641, 1 Taf., 3 figs.)

Verhoeff, C. Zur vergleichenden Morphologie der “Abdominalanhänge” der Coleopteren. (Ent. Nachr., xx, pp. 93–96, 1894. Compare also O. Schwarz and J. Weise’s criticisms in D. Ent. Zeit., pp. 153–157; also pp. 101–109, 155–157. Zool. Anzeiger, pp. 100–106, 1894.)

—— Vergleichende—morphologische Untersuchungen ueber das Abdomen der Endomychiden, etc., und über die Musculature des Copulationsapparates von Triplax. (Archiv f. Naturg., lxi, pp. 213–287, 2 Taf., 1895.)

—— Vergleichende Untersuchungen über die abdominal Segmente der weiblichen Hemiptera-Heteroptera und Homoptera. (Verh. Nat. Ver. Bonn, l, pp. 307–374, 1894.)

Verhoeff, C. Beiträge zur vergleichenden Morphologie des Abdomens der Coccinelliden, etc. (Archiv f. Naturg., lxi, pp. 1–80, 6 figs., 1895.)

Boas, J. E. V. Organe copulateur et accouplement der hanneton. (Oversigt over det K. Danske Vidensk. Selskab Forhand, 1892, Copenhagen, 1893, 1 Pl., pp. 239–261.)

Pérez, J. De l’organe copulateur mâle des Hyménoptères et de sa valeur taxonomique. (Ann. Soc. Ent. France, lxiii, pp. 74–81, Figs., 1894.)

Goddard, Martha Freeman. On the second abdominal segment in a few Libellulidæ. (Proc. Amer. Philos. Soc., xxxv, pp. 205–212, January 11, 1897, 2 Pls.)

Also the writings of Eaton, Emery, Fischer, Forel, Géhin, Godart, Hagen, Joly, Koletani, Loew, Meinert, Mik, Nicolet, Osten Sacken, Pictet, Roussel, Schaeffer (1754), Schaum, Schenk, J. B. Smith, Thompson, Buchanan-White, Brunner von Wattle-Wyll, Weise, Wyenbergh.

The subject of copulation has been treated by Hoffer, Hartig, Schiedeknecht, Verhoeff, etc.

THE ARMATURE OF INSECTS: SETÆ, HAIRS, SCALES, TUBERCLES, ETC.

The cuticula.—The integument is externally either smooth and shining or variously punctured, granulated, tuberculated, striated, or hairy. In certain orders the skin is clothed with flattened setæ or scales, while many forms, as some caterpillars (Figs. 208, 209), beetles (Fig. 210), etc., are protected by spines, horns, etc., these in adult insects often forming secondary sexual characters, usually being more developed in the males than in the females.

The cuticula is not always smooth, but is often finely granulated or even minutely spinulated. On the abdominal segments of Anabrus, as observed by Minot, the cuticula is armed with microscopic conical nodules scattered irregularly over it. They do not correspond, he says, in any way to hairs; for they do not rest over pores, nor did he see any specially modified cells underlying them. “As far as I have observed, they are mere local irregularities, each nodule being apparently supported by some four or six unmodified epidermal cells.” Minot adds that the whole of the cuticula, except the cones just described and the hairs, is divided into numerous minute fields, each of which corresponds to a single cell of the underlying hypodermis. Each field is bounded by a distinct polygonal outline, and its surface is either covered by a large number of extremely minute projecting points, as on the dorsal arch of the segment, or is smooth, as upon the articular membrane and ventral arch. Upon the sides of the dorsal arch and upon the spiracular membrane each field has a projecting spine or sometimes two or even three. (See also pp. 28, 30.)

The cuticle of lepidopterous larvæ has also been described and figured by Minot. In the caterpillars of different groups investigated by him, the cuticle was found to be rough with microscopic teeth or spinules, erect or flattened and scale-like, and either densely crowded or scattered, and affording excellent generic and specific characters. In the slug-worms (Limacodids) we have observed that the cuticula is unusually rough, especially on the spiniferous tubercle of Empretia, Parasa, etc. (Fig. 213, c). The skin of the body between the tubercles is seen to be finely shagreened, due to the presence of fine teeth, which are more or less curved and bent, these teeth arising from a very finely granulated surface (d). The cuticle of neuropterous, trichopterous, and tenthredinid larvæ will probably afford similar cases. The integument of the larva of Datana is, on the black bands, rough and nodulated, the irregular nodules being filled with a black pigment, and forming a layer (p) external to the true cuticula (Fig. 211).

The integument of many insects contains fine canals passing through the chitinous layers and opening externally in minute pores. Certain of the pore-canals communicate with hollow setæ which sit directly over the pores; other pores form the external openings of dermal glands, but in many cases they are empty or only filled with air, and do not have any hairs connected with them. Each of these pores communicates with a hair-forming hypodermal cell, called by Graber a trichogen.

Setæ (“hairs” and bristles).—The setæ of insects are, as in worms, processes of the cuticle originating from certain of the hypodermal cells. They arise either from a ring-like pit, or from a minute tubercle, and are usually situated at the outlet of a pore-canal, which connects with an underlying cell of the hypodermis (Fig. 212). They are, then, bristle or hair-like processes arising from the hypodermis. Where the hairs or setæ are rubbed off, their site is indicated by a minute ring like a follicle in the chitinous integument. The cuticular hair, says Leydig, is in its first condition the secretion of the cellular element of the skin, and a thread-like continuation of the cell-body may rise up through the pore-canal into the centre of the hair, remaining there permanently.

While the setæ are usually simple, they are often branched, plumose, or spinulose, as in larval Hemerobiidæ, Anthrenus, and Dermestes, the larvæ of certain coccinellid beetles, notably Epilachna, and of Cassida, the larvæ of arctians, etc., and in bees (Anthophila, Megachile, Osmia, Colletes, Apis, etc.).

The use of these spinulose, plumose, and twisted hairs in the bees is clearly shown by J. B. Smith, who states that as these insects walk over flowers, the pollen grains adhere to the vestiture, “and this also accounts for the fact, probably noticed by every observant fruit-grower, that bees frequently bury themselves completely in the blossoms, or roll over every part of them. Such insects are after pollen, not honey, and by so rolling about, the pollen grains are brought into contact with and adhere to the surface of the insect.” The syrphid flies also pollenize flowers, the pollenizing of chrysanthemums being effected, as Smith states, by Eristalis tenax, and he adds that the body vestiture of the syrphids “is often composed of spurred and branched hairs.” (For reference to gathering hairs, see p. 45.)

Certain remarkable spines occur in limacodid larvæ, notably Empretia and Adoneta. These we have called caltrops spines, from their resemblance to the caltrops formerly used in repelling the attacks of cavalry. They are largely concerned in producing the poisonous and irritating effects resulting from contact with the caterpillars of these moths, and are situated in scattered groups near the end of the tubercles. A group of three is represented at Fig. 213, e. They are not firmly embedded in the cuticle, but on the contrary appear to become very easily loosened and detached, and they probably, when brought into contact with the skin of any aggressor, burrow underneath, and are probably in part the cause of the continual itching and annoyance occasioned by these creatures. It will be seen by reference to Fig. 213, e′, that the body of the spine is spherical, with one large, elongated, conical spine arising from it, the spherical base being beset with a number of minute, somewhat obtuse spinules.

Glandular hairs and spines.—In some insects occur fine, minute, hollow setæ from which exude, perhaps through pore-canals of extreme fineness, droplets of a clear watery or plasma-like sticky fluid. The club-shaped tenent hairs of the feet of Collembola, and the hairs fringing the feet of Diptera, are modified glandular hairs. Here they serve to give out a sticky fluid enabling the insect to walk on smooth surfaces; they end in a vesicle-like bulbous expansion, which may contain numerous pore-canals. Those of caterpillars were first noticed by Zeller, and Dimmock has particularly described those of the larvæ of Pterophoridæ. They are either club-shaped, or variously forked at the end (Fig. 214, B, a). They are usually replaced after the first larval moult by ordinary, simple, solid, pointed setæ, and their use in caterpillars is as yet unknown. Whether these hairs, as seems most probable, arise from a specialized glandular hypodermal cell, or not, has not yet been discovered.

These temporary fine glandular hairs are probably the homologues of the larger true glandular bristles and spines of the later stages of certain lepidopterous larvæ, which are brightly colored and lead an exposed life, living through a large part of the summer. In these structures the bristles or spines are hollow, filled with a poisonous secretion formed in a single large, or several smaller specialized hypodermal cells situated under the base of the spine. In the venomous spines of Lagoa crispata the poisonous fluid in the larger spines (Figs. 215, C, 216, b) is secreted in several large cells situated at the base of the spine, and this is the usual form. In the finer spines of a large tubercle (Figs. 215, A, 216) there appears to be a differentiation of the hypodermal cells into two kinds, the large, basal deep-seated, setigenous cells (216, sc) and the poison-secreting nuclei (216, pglc) situated nearer the base of the setæ. The spines being filled with poison and breaking into bits in the skin of the hands or neck, cause great irritation and smarting. These nettling or poisonous hairs or spines are especially venomous in the larva of Orgyia, Empretia stimulea, Hyperchiria io, the larvæ of the saturnians (Fig. 217) and lasiocampids, etc. They rarely occur in insects of other orders, though the skin of Telephorus is said by Leydig to bear glandular hairs.

Leydig states that in the stout bristles of Saturnia there is, as in the integument of the body, a homogeneous cuticula, under which is the cellular matrix (hypodermis), and the clear contents (hyaloplasma) are secreted from the blood. The cell-structure of the hairs consist, as in the cells of the body, of spongioplasma and hyaloplasma. Leydig has observed the droplets of the secretion of the caterpillar of Saturnia carpini oozing through distinctly observable pores, and states that there are similar openings in the hairs and scales. Dewitz found easily observable openings at the end of the hair of a large exotic weevil (Fig. 130).

The advanced nymph of Psylla is also armed with clavate glandular hairs (Fig. 178).

The tubercles are outgrowths of the body-walls; they are either smooth, warty, or spiny, as in many caterpillars. While the armature of insects is of little morphological importance, it is evidently of great biological importance, the welfare or even the life of the insect depending upon it; and it varies in each species of insect, especially in Diptera, where the position of even a single seta characterizes the species.

The mode of development of the hairs was first described by Semper. In the pectination of the antenna of Saturnia carpini he observed that the hairs arise, like the scales of the wings, from large round formative-cells lying in the cavity, which send out through the hypodermis and cuticle a long slender process which finally becomes the hair (Fig. 218).

Tactile hairs are those setæ arising over nerve cells or nerve terminations and will be discussed under the organs of sense.

Scales.—In very rare cases the hairs of caterpillars (Fig. 219) are flattened and scale-like, and this passage in the same insect of cylindrical hairs into flattened scale-like ones, shows that the scales are only modified hairs. Also, as we shall see farther on, Semper has proved that their mode of origin is identical. While true scales are characteristic of Synaptera (Thysanura and Colembola), as well as Lepidoptera and Trichoptera, they also occur in the Psocidæ (Amphientomum), in many Coleoptera (Curculionidæ, Cleridæ, Ptinidæ, Dermestidæ, Byrrhidæ, Scarabæidæ, Elateridæ, and Cerambycidæ), and in the Culicidæ, and a few other Diptera, though they are especially characteristic of the Lepidoptera, not a species of this great order being known to be entirely destitute of them.

The scales vary much in shape, but are more or less tile-like, attached to the surface of the body or wing by a short slender pedicel, and are more loosely connected with the integument than the hairs, which are thicker at the base or insertion than beyond.

The markings of the scales, both of Synaptera and Lepidoptera, are very elaborate, consisting of raised lines, ridges, or striæ with transverse ridges between. “The striæ of the transparent scales of Micropteryx are from about 500 to 300 to the millimetre, varying in different species. The opaque scales of Morpho, which show metallic reflections, have about 1400 striæ to the millimetre.” (Kellogg.)

The primary use of scales, as observed by Kellogg, is to protect the body, as seen in Synaptera and Lepidoptera. A nearly as important use is the production of colors and patterns of colors and markings, while in certain butterflies certain scales function as the external openings of dermal scent-glands, and they afford in some cases (as first claimed by Kettelhoit in 1860) generic and specific characters. Spuler has shown that the scales are strengthened by internal chitinous pillars. Burgess has observed in the scales of Danais plexippus that the under surface of the scales is usually smooth, or provided with few and poorly developed ridges, and this has been confirmed by Spuler and by Mayer (Fig. 226).

In the irised and metallic scales the ridges, says Spuler, are not divided into teeth, and they converge at the base to the pedicel and also toward the end of the scale (Micropteryx), or end in a single process beyond the middle (the brass-colored scales of Plusia chrysitis).

The arrangement of the scales on the wings is, in the generalized moths, irregular; in the more specialized forms they are arranged in bands forming groups, and in the most specialized Lepidoptera they are more thickly crowded, overlapping each other and inserted in regular rows crossing the wings, these rows either uniting with each other or running parallel. (Spuler.) The scattered irregular arrangement seen in Micropteryx is also characteristic of the Trichoptera and of Amphientomum.

Development of the scales.—The mode of origin of the scales was first worked out by Semper in 1886, who stated that in the wing of the pupal Sphinx and Saturnia they are seen, in sections, to arise from large roundish cells just under the hypodermis and which have a projection which passes out between the hypodermis (his “epidermis”) cells, expanding into a more or less spherical vesicle, the latter being the first indication of the future scale. He observed that the scales are not all formed at once, but arise one after another, so that on one and the same wing the scales are in different stages of development.

More recently Schaeffer has stated that the scales and also the hairs are evaginations of greatly enlarged hypodermis cells, and still more complete evidence has been afforded by A. G. Mayer (1896). In the wings of Lepidoptera, about three weeks before the imago emerges, certain of the hypodermis cells, which occur at regular intervals, begin to increase in size and to project slightly above the level of the hypodermis; these are Semper’s “formative cells,” and are destined to secrete the scales. They increase in length, and appear as in Fig. 223. In the next stage observed, the projections are much longer (Fig. 224). The hypodermis is now thrown up into a regular series of ridges, which run across the wing. Each ridge, says Mayer, corresponds in position with a row of formative cells, and each furrow with the interval between two adjacent rows. The scales always project from the tops of these ridges. The ground or basal membrane has not participated in this folding, and the deep processes of the hypodermis (prc) that once extended to this membrane have largely disappeared. Figure 225 represents a more advanced stage almost eight days before the emergence of the imago.

The scales are originally filled with protoplasm, which gradually withdraws, leaving behind it little chitinous bars or pillars which serve to bind together the upper and lower surfaces of the scales, and finally the scales become “merely little flattened hollow sacs containing only air.” As Mayer shows (Figs. 226, 227), from the study of scales examined four days before emergence of the butterfly (Danais), “the striations upon the upper surface of the scale are due to a series of parallel longitudinal ridges,” while the under side is usually smooth.

The mode of insertion is seen in Fig. 227. The narrow cylindrical pedicel of the scale is merely, according to Semper, inserted into a minute close-fitting socket, which perforates the wing-membrane, and not into a tube, as Landois supposed. Spuler describes a sort of double sac structure or follicle (Schuppenbalg) which receives the hollow pedicel of the scale. This was originally (1860) observed by F. J. Carl Mayer, but more fully examined by Spuler (Fig. 228) though not detected by A. G. Mayer.

Spinules, hair-scales, hair-fields, and androconia.—Besides the scales, fine spinules occur on the thickened veins of the wings of the Blattidæ, where they resemble fir-cones; also in the Perlidæ, in the Trichoptera, and in the more generalized Lepidoptera (Micropterygidæ and Hepialidæ), occur, as indicated by Spuler, delicate chitinous hollow spinules scarcely one-tenth as long as, and more numerous than, the scales, which sometimes form what he calls “Haftfelds,” or holding areas. These spinules have also been noticed by Kellogg, and by myself in Micropteryx; Kellogg, and also Spuler, have observed them in certain Trichoptera (Hydropsyche). These also occur on the veins, and detached ones near large one-jointed hairs, or hair-scales, said by Kellogg to be striated. Kellogg has detected these scale-hairs, as he calls them, in Panorpa.