GASTEROPODS 341 



VITAL ORGANS, STOMACH, LIVER, RENAL GLANDS, ETC. 



The digestive tract will be found to widen out a short distance 

 back into a crop or stomach, and, continuing still further, to lose 

 itself in a soft, brownish mass within the coiled spire, which is the 

 liver. The very large size of the liver leads one to suspect that 

 Fnlgur and Buccinum must be voracious creatures to need so large 

 an organ for the secretion of bile. In many species of mollusks 

 the stomach and intestines are filled quite solidly, at times, with a 

 gelatinous transparent substance called the crystalline stylet. Just 

 why the digestive tract should be clogged with this substance no 

 one has yet been able to explain, so here again is a chance for 

 original investigation. The intestine curves about after reaching 

 the liver, and conies forward again to appear once more as the 

 rectum, clinging to the inner surface of the free portion of the 

 mantle. 



Closely associated with the liver, but differing slightly in color, 

 is the gonad, or organ in which the genital products are formed. 

 Situated dorsally and forward of the liver and gonad is a large 

 renal gland, which may readily be detected by its peculiar struc- 

 ture. In some forms the kidney is closely associated with the 

 gonad, and seems to cooperate with the latter in the generative 

 functions. 



HEART AND VASCULAR SYSTEM 



To find the heart, make an incision into the body just at the 

 posterior end of the gills. The heart is white and round, and is 

 inclosed within a cavity known as the pericardium ; it has a ven- 

 tricle and one or two auricles, although in Buccinum and Fnlgur 

 there is but one auricle. 



There is nothing remarkable about the vascular system to dis- 

 tinguish it from that of many higher forms of animals. It is, 

 however, not completely closed by which is jneant that the blood 

 is not always contained within arteries or veins, and that it does 

 sometimes flow into other organs and floods certain other body- 

 cavities, although the vascular system of mollusks is by no 

 means so completely open as is that of insects and crustaceans. 



