The radula has been the subject of much study by conchologists, and has furnished the basis for an arrangement of the numerous sections of gasteropods into somewhat well-defined groups. If the observer has a strong glass he will notice that each transverse row of teeth on the ribbon consists of a median or central tooth with several points or "cusps." /Fulgur/ has a median tooth with three cusps; /Buccinum/ one with six. On each side of the median tooth is a lateral tooth, which in /Fulgur/ will be seen to have six cusps, and in /Buccinum/ five. In many patterns of radulæ there is, besides the median and lateral teeth, still another paired row, called the marginals. In the accompanying figures are given some examples which show small sections of lingual ribbons. While all the radulæ of mollusks are capable of being grouped by their general characteristics, yet in no two species of mollusks are the radulæ quite identical. [pg341] 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 /Fulgur/ 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 comes 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 structure. In some forms the kidney is closely associated with the gonad, and seems to coöperate 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 ventricle and one or two auricles, although in /Buccinum/ and /Fulgur/ there is but one auricle.