86 Dr. Burnett on the Development of Viviparous Aphides. 



directly into the intestinal canal, but simply furnishes the material 

 from which the component cells of the said canal and its hepatic 

 diverticula are formed. It also furnishes the material from which 

 the new germs are formed, as already shown. 



8. The heart is formed on the dorsal aspect between the mucous 

 and serous folds. In this way the details of development closely 

 correspond with those of the embryology of the other Articulata 

 which I have studied ; and the subject is all the more interesting, 

 as the germ-masses, from which such development occurs, in no 

 way and at no time structurally resemble true eggs. 



When the embryo is ready to burst from its developing capsule 

 and make its escape from the abdomen of its parent, it is about 

 jgth of an inch in length, or more than eight times the size of 

 the germ at the time when the first traces of development were 

 seen. From this it is evident that, even admitting that these 

 germ-masses are true eggs, the conditions of development are quite 

 different from those of the truly viviparous animals ; such as for 

 instance in Musca, Anthomyia, Sarcophaga, Tachina, Dexia, Mil- 

 toyramma, and others among Dipterous insects* ; or in the vivi- 

 parous reptiles, — for in all these cases of ordinary viviparity, the 

 egg is simply hatched in the body instead of out of it. The egg, 

 moreover, is formed exactly in the same way as though it was to 

 be deposited, and its vitellus contains all the nutritive material 

 required for the development of the egg until the coming forth 

 of the new individual. The abdomen of the mother serves only 

 as a proper nidus or incubatory pouch for its full development. 

 This is true of all the ovo-viviparous animals whatsoever f. 

 With the viviparous Aphides, on the contrary, the developing 

 germ derives its nutritive material from the fatty liquid in which 

 it is bathed, and which fills the abdomen of the parent J. The 

 conditions of development here therefore are more like those in 

 Mammalia, and the whole animal may, in one sense, be regarded 

 as an individualized uterus filled with germs, for the digestive 

 canal, with its appendages, seems to serve only as a kind of 

 laboratory for the conversion of the succulent fluids which the 

 animal extracts from the tree on which it lives, into this fatty 



* See Siebold in Froriep's Neue Notiz. iii. p. 337, and in Wicgmann's 

 Arch. 1838, i. p. 197; also his Observat. quaed. Eutom. &c., p. IS. 



t It is true that in the Scorpionidae the eggs are developed in the ovary, 

 but there is no reason to suppose that the conditions are here different 

 from those of the viviparous Diptera. In Oribates, also, the eggs are de- 

 veloped in a kind of uterus situated directly above the ovipositor, but this 

 appears to be only an incubatory pouch. 



X This fatty matter forms beautiful crystals of margarine, and the crystal- 

 lization may easily be seen to take place. The forms exactly resemble those 

 given by Robin and Verdeil, Traite de Clhm. Anat. et Physiol, pi. 38. 

 fig. 2 A.' Paris, 1853. 



