Dr. Burnett on the Development of Viviparous Aphides. 67 
rous 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 materi- 
al 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 indus or incubatory pouch for its full development. 
This is true of all the the ovo-viviparous animals whatsoever.* 
ith 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.t The 
conditions of development here therefore are more like those in 
ammalia, 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 labo- 
tatory for the conversion of the succulent fluids which the ani- 
mal extracts from the tree on which it lives, into this fatty liquid 
=~ which the increase and development of the germs take 
ace, 
Pi points which have here been made out. In the first place, 
it is evident that the germs which develop these forms are not true 
‘ss. ‘They have none of the structural characteristics of eggs, 
Such as a vitellus, a germinative vesicle and dot; on the other 
* It is true that in the Scorpionidae, the eggs are developed in the ovary, but 
-.- 800 reason to suppose that the conditions are here different from those of the 
Parous Diptera, 
es, also, the eggs are developed in a kind of uterus situated directly 
a 
above the ovipositor, but. this pears to be only an incubatory pouch. 
shown that in these animals the rate of increase is so great that 
ine he eleven !! 
érby and Spence, Introduction to Entomology, i, p. 175. _ 
