INTRODUCTION. 11 
We will not mention the other parts of the alimentary canal in 
insects. We will only speak of some of the appendages of this 
apparatus. 
The salivary glands pour into the digestive tube a liquid, gene- 
rally colourless, which, from the place where it is secreted, and its 
alkaline nature, corresponds to the saliva in vertebrate animals. It 
is this liquid which comes in the form of drops from the tongue of 
sucking insects. 
These vessels are always two in number. Their form is as 
variable as complicated. The most simple is that of a closed 
flexible tube, generally rolled into a ball, 
and opening on the sides of the ceso- 
phagus. 
- At the posterior extremity of the 
chylific ventricle are inserted a vari- 
able number of capillary tubes, usually 
elongated and flexible, and terminating 
in culs-de-sac. heir colour, which de- 
pends on the liquid which they contain, 
is sometimes white, but more frequently 
brown, blackish, or green. They appear 
to be composed of a very slight and deli- 
cate membrane, as they are very easily 
torn, and nothing is more difficult than 
to unroll and to disengage them from 
the fatty or other tissues by which they 
are enveloped. 
The function of these vessels is un- 
certain. Cuvier and Léon Dufour sup- 
posed them to be analogous to the liver, 
and on that account they have been called 
biliary vessels; but as this opinion is not 
generally held, it has been agreed to call 
them the Malpighian vessels, after the 
name of their discoverer. 
According to M. Lacordaire, their func- BE Ge Te eee ae 
tions vary with their position. When wa 
they enter the chylific ventricle, they furnish only bile; bile and 

