34 
BRITISH APHIDES. 
pyloric entrances both, at one end, whilst a blind 
annular tube proceeds from the other end of the 
stomach, from the walls of which tube several bead- 
like vessels depend, which Dufour refers to the biliary 
system, ‘‘vesicules biliares.” 
Sir J. Lubbock says that in Pentatoma (Hetero- 
ptera) the biliary vessels pour their contents into the 
rectum below the ilium, but in no other group of 
insects, except, perhaps, in the Homoptera, do the 
biliary vessels open elsewhere than at the anterior end 
of the ilium, or the colon. 
RESPIRATORY SYSTEM. 
The trachese in Aphides are very numerous, and are 
disposed over almost every part of the body. They are 
particularly numerous round the bases of the cornicles, 
but they do not appear to be at all connected with 
them. They also are well developed in the thoracic 
region, and accompany the great nervures of the 
wings, without apparently opening into them. These 
last tubes may sometimes be seen, after the fresh wings 
have emerged from the wing cases of the pupae, and 
whilst the membrane is soft and supple ; but the won- 
derful expansion and growth of the wing, certainly in 
Aphis, is not caused by air being pumped into these 
nervures or by dilatation of the tracheae. 
The ovarian system is well supplied with these 
vessels for aerification. 
As in other insects, the tracheae start, in trunks of 
considerable diameter, from certain pulmonary sacs, 
which have their communication with the outer air, 
through their respective stomata. These large trunks 
abruptly give off numerous finer tubes, which form 
distinct tufts in each ring of the body. A large tube 
takes a zig-zag form down each side of the back, into 
which the finer tracheae anastomose. 
In many transparent species these tubes appear like 
