THE FOOD OF THE COMMON SEA-URCHIN. 
BY J. W. DAWSON, LL.D. 
THoueu this creature* is so common on the north-eastern 
coasts of North America, the nature of its food does not 
seem to be generally known. In dissecting some speci- 
mens collected at Tadoussac, Canada, last summer, I 
found the intestine full of small round pellets, which 
proved to be made up of the minute confervoid sea-weeds 
that grow on submerged rocks, mixed with many diatoms 
and remains of small sponges. It would thus appear that 
the curious apparatus of jaws and teeth possessed by this 
creature is used in a kind of browsing or grazing pro- 
cess, by which it scrapes from submarine rocks the more 
minute sea-weeds which cling to them, and forms these 
into solid balls, which are swallowed, and in this state 
passed through the intestinal canal, where they may be 
found in all stages of digestion. The sea-urchin is thus a 
kind of submarine rodent, in so far as its habits are con- 
cerned. From these pellets the microscopist may, after di- 
gesting them in nitric acid, obtain great numbers of beau- 
tiful diatoms (or microscopic plants, for a long time classed 
with the Infusoria), which are collected by the animal with 
its food, and whose silicious crusts escape the digestive 
