32 
BEITISH APHIDES. 
(b) internal anatomy. 
The dissection and manipulation of Aphides present 
peculiar difficulties, partly on account of their diminu- 
tive size, and partly from the extreme tenderness of 
their viscera, which in great measure break up by im- 
mersion in fluids employed in dissection, which do not 
approach the density of the surrounding animal juices. 
I regret that our knowledge of the internal anatomy of 
Aphis is yet far from complete ; nevertheless, I may 
be permitted to add some observations I have made, 
with reference to their alimentary, circulatory, and 
respiratory systems. 
THE ALIMENTARY SYSTEM. 
Aphides possess a gullet of some length, but of 
small diameter. It ends in a considerable dilatation 
or stomach, which apparently has no villous coat. 
Usually it is charged with a pulpy mass, which seems 
to gather into pellets, which are transferred to a 
long intestinal tube for assimilation. Proceeding from 
the lower end of this pouch, the alimentary tube 
descends to a broader sac, which, having its opening 
at the anus, may be regarded as the rectum, or the 
caecum. 
The alimentary canal varies greatly in length. In 
some genera it attains twice or thrice the length of the 
body, within which it undergoes several convolutions. 
Some species show it shorter, and apparently looped 
back, before communicating with the rectum. In 
other cases it is very short and comparatively straight. 
In Plate C, figs. 1 and 5, the alimentary apparatus is 
represented, but the drawings do not profess to show 
the exact form of the folds as they lie in the living 
insect. 
