The inferior edge of each channel bears a series of processes by which one galea is strongly tied to the other; while its superior edge carries one or more series of flat processes which overlap the corresponding processes of the other side. The outer surface carries hairs and 'borers' (opotrypes), the latter restricted to the tip. The borers are simple in Sphinx. When well developed they appear to act by piercing the nectaries of flowers or even pulpy fruits (e. g. as by Ophideres), and it is possible that they may also be to a certain extent organs of touch. The labium is reduced to a membrane between the bases of the maxillae. Its palps are three-jointed. The terminal joint, though small, is moveable. The second is deep, compressed and grooved where it fits round the maxilla of its side, and the first joint narrows to its base which is attached to a small cone3.
1 Newport (article Insecta) calls the first of these two spiracles, mesothoracic (p. 923), the second, metathoracic (p. 924); and Muller-Blumenau uses the same expressions, connecting the spiracles of the imago with the two closed thoracic spiracles he discovered in an aquatic caterpillar. See ante, p. 150, and p. 199 of paper quoted. In all the specimens I have examined they are situated as above described.
2 The prominence figured by Newport (article quoted) Fig. 377, as labrum, is a process of the clypeus from which a muscle takes origin. The parts designated mandibles by him (as they are also by Savigny) are really the lateral lobes of the labrum according to Walter. The only pupa of S. Ligustri at my command in a fit state to decide the question appears to corroborate Walter's view.
3 Walter has shown that in certain species of Micropteryx (Tineinae) there is a hinged and toothed mandible; a maxilla with moveable cardo and stipes, six-jointed palp, a thin lacinia and
Changes have taken place in the internal organs. The supra- and sub-oeso-phageal ganglia have coalesced round the oesophagus. The mesothoracic ganglion appears to abortl, the prothoracic persists and is approximated to the metathoracic which has coalesced with the first abdominal. The second and third abdominal ganglia abort, but the nerves which they give off persist. The abdominal ganglia of the imago correspond to the four last ganglia of the caterpillar. A remarkable structure, the chorda supraspinalis, overlies the abdominal ganglia, extending from the spot where the nerves arise from the sixth, an aborted ganglion, to the last ganglion. It is well-developed in the imago, and has been found by Burger in a large number of Lepidoptera. It is triangular in section and is intimately united by one angle to the neurilemma of the nerve cord whilst lateral muscles are attached to its two other angles extending thence to the abdominal walls. It is composed either of reticular cell-tissue with intervening jelly, or of vesicular cells. The chorda forms a strong attachment for the muscles, and the latter roof in the ventral blood-sinus (see under Cockroach, p. 144). There are vesicles developed on the tracheal branches in the abdomen.
In the digestive tract there is a pharyngeal sac which can be dilated and contracted by systems of muscles. The oesophagus is long, and has at its stomachal end a non-pedunculated sucking stomach. The chylific stomach of the caterpillar is much reduced. The Malpighian vessels have lost their bead-like caeca. The intestine is long and the colon, as in many Lepidoptera, has a large dorsal caecum.
The testis is single externally, the two embryonic testes having become enveloped in a common sheath, as is often the case in Lepidoptera 2. But there are two vasa deferentia: they are long much contorted tubes, and each duct receives an accessory tubular gland.
Each ovary consists of four long convoluted ovarian tubules united terminally by a ligament, both inter se and to the dorsal wall of the abdomen. The bursa copulatrix is large and pyriform, and a slender canal starts from its neck on the ventral anterior surface, curves round the neck and enters the side of the vagina. At its entrance a slender caecum is attached to the vagina which probably represents a spermatheca. There are two accessory tubular glands which dilate each into a pyriform enlargement, then fuse, and their common duct opens dorsally into the vagina near its exit. This exit is immediately below the anus3. enlarged galea; a labium with mentum, three-jointed palps, paraglossae and ligula. In other species of the same genus the mandible is a simple lobe, the laciniae of the two maxillae are lost, and the galeae are transformed into more or less typical antliae capable of being coiled up and closely united, and there are no paraglossae. Mandibles as more or less simple lobes articulated to the head appear to exist in most Micro-letpidoptera.
1 So thinks (Newport Phil. Trans. 1834, P. 394), but with reference to Vanessa Urticae he says (p. 416) that the prothoracic and mesothoracic, his second and third, ganglia fuse. Herold states the same fact with reference to Pieris Brassicae.
2 Cholodkowsky has shown that when the external capsule is removed, the apparently single testis consists of eight testicular follicles, four to each vas deferens. The follicles are arranged in various ways within the sheath. Hepialus Humuli retains the testis in the primitive condition, i. e. four free follicles on each side. In Pygaera anachoreta, etc, each set of follicles is contained within a separate capsule: but in most Lepidoptera the follicles of both sides are contained in a common capsule.
3 There can be little doubt that the canal connecting the bursa copulatrix to the vagina, itself represents the primitive vagina. The aperture of the bursa is in the typical position of the vaginal aperture. The canal in question has to pass round the neck of the bursa to gain its destination. The bursa in all other insects is a dorsally-placed appendage to the vagina. These
The origin of a perfect metamorphosis, such as that of Sphinx, with three well-marked stages, larva, pupa, and imago, is probably due to the operation of more than one cause. The Cockroach is an example of an insect which always lives from birth to the adult state in the same manner and under the same conditions; and this is the case with all Ametabolous Insecta. At birth such insects differ from the adult only in a few points, and the differences are gradually abolished. On the other hand, the differences between a caterpillar and a butterfly are very great, and the change from one state to the other is effected in an abrupt manner. It has been pointed out by Balfour (Comp. Embryology, i. p. 353) that a pupa-stage might easily arise (1) from a change at first small, then greater, in the character of the mouth-parts which would necessitate a more or less prolonged period of quiescence, the more prolonged the greater the change; (2) from the operation of climate and other natural causes on such a period of quiescence.
The question however is a very difficult and complex one, impossible to treat in a short compass, and the student must refer to the list of works given below relating to the Metamorphosis and Genealogy of Insecta. But it must be carefully borne in mind that, among the Micro-Lepidoptera, certain minute moths are known with mouth-parts conformed to the type of biting mouth-parts (note, p. 159); that it is possible that the period of pupation is accompanied by more than one ecdysis, and is therefore essentially a period of abbreviated development; that in some Hymenop-tera Aculeata there is, as it were, a preparatory stage previous to the true pupa-stage (Packard, Guide to Study of Insects, 1872, p. 66) j that the changes from the larval mouth-parts to those of the adult are not so very great in all Metabolay e. g. in the Tenthredinidae j and that grades may be traced among Metabola, e. g. the Trichoptera and some Neuroptera afford examples of a comparatively simple perfect metamorphosis, the Lepidoptera a more complex example; whilst in some Hymenoptera, and especially in the Diptera as a class, the metamorphic changes are of a very profound character.
Nor must it be forgotten that our knowledge of many details of anatomy, embryology and of life-histories is still very imperfect.
British Butterflies and their Transformations; Humphreys and Westwood, London, 1841. British Moths, lid., 2 vols., 1843-45. Tineina (Insecta Britan-nica), Stainton, London, 1842. Natural History of Tineina, Id., 13 vols., London, 1855-73. Butterflies, etc, Scudder, New York, 1881.
Anatomy of Danais Archippus.Burgess, Anniv. Memoirs, Boston Soc. Nat. Hist. 1880. Cossus. Lyonet, Ouvrage posthume (see p. 156, ante), Paris, 1832.
Sphingidae.Butler, Tr. Z. S. ix. 1877. Anatomy of, etc, Baltzer, A. N. 30, 1864.
Mouth-parts.Kirbach, A. N. 50, 1884. Walter, Beitrage, J. Z. xviii. 1884. Antlia. Breitenbach, J. Z. xv. 1882. In Ophideres fullonica. Darwin, Q. J. M. xv. 1875.
Mode of Action of mouth-parts. Burgess, Amer. Naturalist, xiv, 1880.
Palpus maxillorum.Walter, J. Z. xviii. 1884.
Wing and Scales.Semper, Z. W. Z. viii. 1857; Deschamps, A. Sc. N. (2) iii. 1835; cf. Dimmock, Psyche, iv. 1883. On Wings in Insecta. Adolph, Nova three facts point strongly to the conclusion stated. The vaginal aperture below the anus is therefore secondary, but the mode in which it arises has not been worked out. It should be noted that in the caterpillar the somites in this posterior region are much abbreviated.
Acta, 41, 1879; 46, 1884; Amans, Comparaisons des organesdu vol dans la seVie animale, A. Sc. N. (6) xix. 1885.
Stridulation of Acherontia. Moseley, Nature, vi. 1872.
Neivous system. Chorda supraspinalis. Burger, Arch. Zool. Niederland. iii. 1876-77. Cattie, Z. W. Z. xxxv. 1881. Nussbaum, Z. A. viii. 1884, pp. 17, 48. See works cited ante, pp. 152, 156.
Eye. Carriere, Sehorgane der Thiere, pp. 152, 186, Munchen und Leipzig, 1885. Grenacher, Sehorgan der Arthropoden, Gottingen, 1879, p. 103. Carriere, Q. J. M. xxiv. 1884; Id. Z. A. ix. 1886, and Hickson, Q. J. M. xxv. 1885.
Malpighian vessels.Cholodkowsky, C. R. xcviii., xcix. 1884.
Stigmata.Krancher, Z. W. Z. xxxv. 1880.
Sex apparatus in Nematois metallicus. Cholodkowsky, Z. W. Z. xlii. 1885.
Testis.Cholodkowsky, Z. A. iii. 1880; vii. 1884. Clasping organs of Rho-palocera. Gosse, Tr. L. Sc. (2) ii. 1883; White, Ibid. i. 1879. Connection of genitalia to heart. Landois, Z. W. Z. xiii. 1863.
Ovary.Brandt, Das Ei, Leipzig, 1878. Female apertures. De Lacaze-Duthiers, A. Sc. N. (3) xix. 1853.
Metamorphosis.Martin Duncan, Transformation of Insects (ed. iii.), Cassel and Co., London (n. d.). Sir John Lubbock, Metamorphosis of Insects (Nature Series), 1874. Balfour, Comp. Embryology, i. p. 348 et seqq. Keferstein, Betrachtungen uber die Entwickelungsgeschichte der Schmetterlinge u. deren Variation, Erfurt, 1880 (not seen).
Genealogy of Insecta.Packard, American Naturalist, xvii. 1883. Brauer, Verhandl. K. K. zool. bot. Gesellschaft, Wien, xix. 1869; xxviii. 1878. Id. Sys-tematisch. Zoologisch. Studien, SB. Akad. Wien, xci. Abth. 1, 1885; see Emery, Biol. Centralblatt, v. 1884-85. Mayer, J. Z. x. 1876. Cf. Wood Mason, Trans. Ent, Soc. 1879.