THE YOUNG. 
83 
being those situated at the apex of the abdomen, from 
whence they are expelled through the vulva, in an ex- 
ceptional manner, that is to say, tail foremost. 
The young, during birth, have all their extremities 
disposed parallel to the axis of their bodies, and appear 
to be lubricated with a fluid which gives as smooth a 
surface as will permit the antennae and legs freely to 
pass point foremost. In Pemphigus the foetus appears 
to be enclosed in an exceedingly fine membrane, which 
is cast in the course of a few minutes, after which the 
limbs extricate themselves one by one. At the time of 
birth the young rose Aphis exhibits peculiar rapid 
pulsations throughout the body, during which action 
air is absorbed into the tracheae. As these dilate the 
insect visibly grows, and that long before it has taken 
the least nourishment. Even in this early stage the 
germs of the next generation may be clearly traced. 
It is to be remarked that Aphides of the second 
generation show a small but decided advance in 
development over those extruded from the egg. The 
antennae are longer, and in many cases show an increase 
from five to six joints. The legs and nectaries are 
more elongated, and there is also some indication of a 
tail. As the insect grows, it passes more into the 
ordinary larval form, minute alterations probably being 
effected at the time of each moult of skin, at which 
time the greatest increase of size also takes place. 
The number of young Aphides born from a single 
individual varies with the species, and the same remark 
applies to the number of broods to be comprised in a 
cycle. I have counted as many as twenty-five embryos 
in the body of the female of the viviparous Siphono- 
phora roscBi and all of these were in a more or less 
forward condition of development. Numerous other 
pseudova were there to prove that this was far from 
her limit of reproduction. As to the number of broods, 
there is a considerable variation also ; some species 
probably are confined to one, whilst other kinds reach 
to twenty, or, it is stated, to as many as ninety. 
