COMPARATIVE ZOOLOGY. 
124 
Thus, in Polyps it is represented by yellowish cells lining 
the stomacli; 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 gaU-bladder , 
which is simply a reservoir for the bile when not wanted. 
The so-called liver of Invertebrates is probably more 
Fig. 92.—Liver of the Dog, F, F; D, duodenum aud iutestiues; P, pancreas; r, 
spleen; e, 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 t diaphragm; VC, vena cava; C, heart. 
