306 



SYSTEMATIC ZOOLOGY 



part of this tube may be expanded into a glandular food- 

 reservoir or crop (birds). 



In some fishes and Amphibia the stomach is hardly 

 differentiated from the oesophagus, but in other forms it 

 is well developed, with muscular and glandular walls. It 

 may even be divided into several portions. Thus in 



FIG. 114. Diagram of the digestive tract of a mammal. 6, brain; d, dia- 

 phragm; h, heart; ?', intestine; k, kidney; I, liver; o, oesophagus; p, pan- 

 creas; s, stomach; sp, spleen; v, vent. 



birds (fig. 147) we frequently find two parts, one chiefly 

 glandular, while the other (gizzard) is extremely muscu- 

 lar. In the ruminants (p. 385) the specialization is 

 carried farther, and we find four divisions to the or- 

 gan. 



While some absorption of food takes place in the stom- 

 ach, the intestine is the chief absorptive portion of the 

 alimentary canal. In some vertebrates it is short and 

 straight, in others long and convoluted, there being usu- 

 ally a correlation between length of intestine and the 

 character of the food, this region being longer in the 

 vegetable feeders. Increased absorptive surface is ob- 

 tained in several ways, in addition to lengthening of the 

 intestine. In the lower Ichthyopsida this is accomplished 



