516 



PISCES FISHES. 



winch the digested aliment may be spread, for the purpose of 

 absorbing its nutritive portions. In these tribes a spiral valve 

 (Jig' 236, A) winds in close turns from the pyloric to the anal 

 extremity of the capacious intestine ; so that, although externally 

 the intestine appears short in proportion to the size of the animal, 

 its mucous lining is exceedingly extensive. 



Fis- 227. 



(548.) In addition to the biliary secretion which we have met 

 with in the lower animals, another system of chylopoietic glands for 

 the first time makes its appearance in the class before us, from which 

 a fluid termed the pancreatic is poured into the intestine. In the 

 osseous fishes this viscus presents the simplest condition of a gland, 

 consisting of simple caeca (fig. 227, n, n) ; sometimes, as in the 

 Perch, only three in number ; at others, as for instance in the 

 Salmonida, extremely numerous. From these appendages a glairy 

 fluid, resembling saliva in composition, is abundantly secreted, 

 and becomes mixed with the bile immediately upon its entrance 

 into the intestine. 



In the cartilaginous fishes, such as Sharks and Rays, the pan- 

 creas exhibits a more perfect developement, and already presents 

 the appearance of a conglomerate gland (fig. 236, /), from which 

 the pancreatic fluid is conveyed into the intestine through a com- 

 mon duct. 



