58 



DIGESTION IN INSECTS AND BIRDS. 



Fig. 8. 



and is little more than a mere dilatation of the alimentary canal. But 

 Analogous ar- when, as among the herbivora and granivora, 

 SffS*ni? there is a g reat differ ence Between the form 

 mais. of the food received and the form of the tis- 



sues to be made, the digestive sac no longer presents 

 such a simple structure, but is parted off into distinct 

 regions, or is actually converted into distinct organs. 

 Thus, in the insect digestive tract shown in Fig. 8, 



Digestives- a is the P hal 7 nx > * the oesophagus, lead- 

 partmcnts of ing into a crop or insalivatory pouch, c, and 

 this into the gizzard, d, the function of which 

 is to rasp up and abrade the more resisting portions of 

 the food, which, when this is accomplished, passes into 

 the true stomach, e, and from thence into the intestine, g. 

 The delicate vessels about f are supposed to be biliary 

 tubes, and h glandular secreting organs. 



T-, , f i Digestive tract of a car- 



Even in these cases of minute organization, the mu- nivorous beetle. 



cous structure remains the same as in larger animals of the same mode 



of life. The photographic represetita- 

 tion in Fig. 9 displays the same retic- 

 ulated appearance in the stomach of 

 the carnivorous beetle as has been de- 

 scribed in the case of that of man; 

 and undoubtedly, with similarity of 

 structure there is similarity in the man- 

 ner of action. 



A regional division of 

 the digestive apparatus 

 is also presented in the 

 case of many birds, as 

 is shown in the photo- 

 graphic representation, 



Fig. 10, in which we have the digestive tract of the corn- 

 Digestive com- mon fow1 ' a be?in S the oesophag* 8 leadin g 

 into the insalivating pouch or crop, 



which empties into the stomach, c, 

 and this into the gizzard, d. In the stomach, 

 which is relatively small, the digesting material 

 is mingled with the gastric juice before being 

 submitted to the action of the gizzard. From 

 the gizzard it is passed into the small intestine 

 y, f. In the figure, e is the liver, # , g, the cceca, 

 and h the cloaca. Dlgcstive tract of th: common fowl 



Fig. 10. 



Mucousmembraoeachofacarnivo- 



partments of 



