208 



PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



always, however, a gullet, craw, gizzard, large and small intestines, and 

 numerous glandular appendages may be recognized (Fig. 63). 



In the vermiform larvae the alimentary canal is a straight tube passing 

 from one end of the body to the other, the dilatations which represent 

 the stomach and crop appearing later. Caeca are also then present, and 

 there is hence a division into small and large intestines. In mandibulate 



insects, as in the wasps and beetles, 

 the crop and stomach are glandular, 

 and the gizzard, unlike that of birds, 

 is placed above the stomach, and 

 has muscular walls and a chitinous 

 lining-membrane. In insects the 

 form of the liver has again returned 

 to that of long, slender tubes, pouring 

 their secretion into the intestine, 

 and which are believed to represent 

 biliary canals (Fig. 63). In carniv- 

 orous insects the crop and gizzard 

 and large intestine are less developed 

 than in those which feed on vege- 



Fio. 63. DIGESTIVE APPARATUS OF HONEY- 

 BEE (Apis mellifica), AFTER LEON Du- 

 FOUR. 



rjl, salivary gland; rjlv, poison-gland: (, sting; oe, 

 oesophagus ; vm, vasa malpjghii ; c, colon ; r, rectum ; 

 ingl, crop. 



FIG. 64. ANATOMY OF THE OYSTER. 



(Perrier). 



F, moxith ; E. stomach : I. intestine ; A. anus ; 

 GG', nervous ganglia; MT, mantle; B, branchiae. 



table food, thus indicating in them the first appearance of the distinction 

 between the herbivorous and carnivorous animals, showing that the com- 

 plexit}'" of the alimentary canal is in direct proportion to the complexity 

 of the food. The intestine is narrow, convoluted, and but seldom has a 

 mesentery; distinctions between small and large intestines are but imper- 



