A. J. Grove 
23 
its fellow of the opposite side but no distinct fusion takes place between 
them. 
The two tracheae which pass to each of the first pair of legs arise 
from the last but two and last of these branches—the most anterior 
one passing to the end of the leg, and the other continuing only to 
the end of the femur. 
The second thoracic stigmata. Near the commencement of the main 
ventral transverse trachea arising from the second thoracic stigma on 
each side, a branch is given off which passes directly posteriorly and 
enters the third leg. 
This trachea traverses the leg to its extremity. A little farther 
along the main trachea, another branch is given off in an anterior 
direction ; from this a sub-branch arises, which turns posteriorly and 
enters the second leg. In the latter case, however, the trachea only 
extends to the end of the femur. Still a little farther along the main 
trachea another branch is given off which passes directly backwards and 
enters the third leg, but only continues to the end of the femur. The 
remaining branches from this transverse trachea connecting the second 
pair of thoracic stigmata, pass to the region traversed by it. 
The distribution of the branches to the legs yields reliable evidence 
—apart from their position—that the two pairs of thoracic stigmata 
belong to the first and third thoracic segments—each thoracic stigma 
contributing one branch for the aeration of the second pair of legs to 
take the place of the tracheae which would arise from the stigmata, 
were they present, of the second thoracic segment. 
The Reproductive System. 
The reproduction of the Aphides in this stage of their life history 
has attracted a great deal of attention from the fact that it exhibits the 
peculiarity of parthenogenetic reproduction. This being so, there is 
abundant literature on the subject, but it all—or nearly all—deals with 
the actual segmentation of the eggs, or with the nuclear changes thus 
involved. 
The morphology of the reproductive system is so simple that the 
figures given by the earliest investigators still remain almost unaltered 
to-day. 
Dufour (1833), Buekton (1875—1882), Witlaczil (1882) and others 
give accounts and illustrations of the appearance of this system. 
The reproductive system (Text Fig. 15) offers no very remarkable 
