ALIMENTARY ORGANS. 27 



behind this is a second stomach, the interior of which 

 is furnished with horny plates for the comminution 

 of the food ; this, from analogy, has received the name 

 of gizzard. After passing through this organ, the 

 food advances to the third stomach, in which the 

 actual work of digestion appears to commence, as its 

 walls are usually provided with glandular organs which 

 appear to secrete a sort of gastric juice. On quitting 

 the stomach, the alimentary canal regains its tubular 

 form, constituting the true intestine, which, after 

 twisting about in the cavity of the abdomen to a 

 certain extent, leads down to the anal aperture. The 

 amount of convolution to which the intestine is sub- 

 jected, depends of course upon its length in com- 

 parison with that of the body, and this, as in the 

 higher animals, is dependent upon the nature of the 

 food. Thus carnivorous insects, and those which 

 feed upon fluid matters which are easily assimilated, 

 do not require any great length of intestine, and in 

 them the whole canal is often less than twice the 

 length of the body, whilst in those which feed upon 

 solid vegetable matters, requiring a great amount of 

 preparation before they will yield the nutriment they 

 contain, the intestine acquires so great a length that 

 the alimentary canal is frequently eight times as long 

 as the body. 



In sucking insects the crop and gizzard are often 

 deficient, but in place of the former, the oesophagus is 

 furnished with a lateral dilatation, sometimes united 

 to it only by a long tube ; this is called the sucking 

 stomach, as its expansion is supposed to assist these 

 insects in pumping up their food. 



Appended to the alimentary canal we find certain 

 organs, whose office is the secretion of particular fluids 



c 2 



