CHYLIFICATION. 



205 



The total length of the intestinal tube differs 

 much in different animals, being in general, as 

 already stated, smaller in the carnivorous tribes, 

 than in those which feed on substances of diffi- 

 cult digestion, or affording but little nourishment. 

 In these latter animals, the intestine is always of 

 great length, exceeding that of the body many 

 times ; hence it is obliged to be folded into a 

 spiral or serpentine course, forming many con- 

 volutions in the abdominal cavity. Sometimes, 

 probably for greater convenience of package, 

 instead of these numerous convolutions, a similar 

 effect of increasing the surface of the inner 

 membrane is obtained by raising it into a great 

 number of folds, which project into the cavity. 

 These folds are often of considerable breadth, 

 contributing not only to the extension of the 

 surface for secretion and absorption, but also to 

 the detention of the materials, with a view to 

 their more complete elaboration. Remarkable 

 examples of this kind of struc- 

 ture occur in most of the carti- 

 laginous fishes, when the inner 

 coat of the large intestine is ex- 

 panded into a broad fold, which, 

 as is seen in Fig. 316, repre- 

 senting this stRicture in the in- 

 terior of the intestine of the 

 shark, takes a spiral course ; and 

 this is continued nearly the whole 



