124 



COMPARATIVE ZOOLOGY. 



Thns, in Polyps it is represented by yellowish cells lining 

 the stomach ; in Insects, by cells in the wall of the stom- 

 ach ; in Mollusks, by a cluster of sacs, or follicles, forming 

 a loose compound gland. In Vertebrates, the liver is well 

 defined, and composed of a multitude of lobules (which 

 give it a granular appearance) arranged on the capillary 

 veins, like grapes on a stem, and containing nucleated 

 secreting cells. It is of variable shape, but usually two, 

 three, or five lobed, and is centrally situated in Mam- 

 mals, just below the diaphragm. In most Vertebrates, 

 there is an appendage to the liver, called the gall-lladder, 

 which is simply a reservoir for the bile when not wanted. 

 The so-called liver of Invertebrates is probably more 



Fio. 92. Liver of the Dog, F, F; D, duodenum and intestines; P, pancreas; r, 

 spleen ; , stomach , /, rectum ; R, right kidney ; B, gall-bladder ; ch, cystic 

 duct; F, lobe of liver dissected to show distribution of portal vein, VP, and 

 hepatic veiu, vh; d, diaphragm; VC, vena cava; C, heart. 



