Insects.—De Geer has described the incubation of the Earwig, and the care of the brood by the female. The cases of the social Hymenoptera, &c., are universally known.
Spiders.—The care of the female spider for her eggs is well known.
Crustaceans.—The Crayfish hatches and subsequently protects her young. Mysis, Diastylis (Cuma), and some Isopods hatch their eggs. Gammarus locusta is followed about by her brood, which shelter beneath her when alarmed. Podocerus capillatus builds a nest among corallines. Several of the Caprellidæ hatch or otherwise protect their young. All these, except the Crayfish, are marine; the eggs commonly fewer than usual.
Echinoderms.—Many cases of “marsupial development” have been recorded in the species of the Southern seas. Here development, contrary to the rule in Echinodermata, is direct.
[188] The minute and early larvæ of Tœnia and Distomum may appear to contradict this statement. They really inhabit the film of water which spreads over wet grass, though they are capable of enduring dry conditions for a short time, like Rotifers and many Infusoria.
[189] It is possible that the curious cases of agamogenetic reproduction of the larvæ of Aphis, Cecidomyia, and Chironomus are vestiges of the original fertility of Insect larvæ.
[190] “Alia vero semen adhuc imperfectum et immaturatum recludunt, incrementum et perfectionem, sive maturitatem, soris acquisiturum; ut plurima genera piscium, ranæ, item mollia, crustata, testacea, et cochleæ: quorum ova primum exposita sunt, veluti origines duntaxat, inceptiones et vitelli; qui postea albumina sibi ipsis circum circa induunt; tandemque alimentum sibi attrahentes, concoquentes et apponentes, in perfectum semen atque ovum evadunt. Talia sunt insectorum semina (vermes ab Aristotele dicta) quæ initio imperfecte edita sibi victum quærunt indeque nutriuntur et augentur, de eruca in aureliam; de ovo imperfecto in perfectum ovum et semen.”—De generatione, Exc. II., p. 183 (1666). Viallanes justifies this view by applying it to the histolysis and regeneration of the tissues in Diptera. But these remarkable changes are surely secondary, adaptive, and peculiar, like the footless maggot itself, whose conversion into a swift-flying imago renders necessary so complete a reconstruction.
[191] The reader is recommended to refer to Fritz Müller’s Facts and Arguments for Darwin, especially chap. xi.; to Balfour’s Embryology, Vol. II., chap. xiii., sect. ii.; and to Lubbock’s Origin and Metamorphoses of Insects.
[192] Those who care to see a bold experiment of this kind may refer to Haeckel’s Schöpfungsgeschichte.
[193] Comp. Embryology, Vol. I., p. 451.