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 ; the inner coat 

 of the large intestine being ex- 

 panded into a broad fold, which, 

 as is seen in Fig. 316, repre- 

 senting this structure in the in- 

 terior of the intestine of the 

 Shark, takes a spiral course ; and 

 this is continued nearly the whole 



