THE BIVALVES 



3379 



MARGIN OF MANTLE OF PECTEN, SHOWING TENTACLES 

 AND EYES (somewhat magnified). 



stands far above all other mollusks, and its artificial cultivation was practiced 

 by the ancient Romans, and at the present time forms a most important industry 

 in many parts of the globe. The oyster is very prolific, a single individual 

 of the common species having been estimated to contain over a million em- 

 bryos, while the American form is 

 said to discharge ten times as 

 many; O. edulis is not full grown 

 until about five to seven years old. 

 Oysters are incapable of motion, 

 and attach themselves to other 

 shells, rocks, and other substances 

 b) r the convex or deeper valve. 

 During May, June, and July, the 

 eggs are discharged into the gills, 

 where they remain until hatched; 



and it is during this period that oysters are out of season. Oysters are cosmopolitan; 

 wherever there is a rocky coast, excepting in Arctic climates, they are sure to 

 be found. They are irregular in their growth, and consequently the determination 



of the species is a matter 

 of difficulty. The pec- 

 tens or scallop shells 

 {Pectinidce) are remark- 

 able for the variety and 

 beauty of their colora- 

 tion and sculpture. In 

 most species the shells 

 are nearly equivalve; but 



in a few, of which the 

 common edible scallop is 

 an example, the right 

 valve is convex, and the 

 left flat. One species 

 {Pecten Jacob ecus) of the 

 Mediterranean was worn 

 as a badge by pilgrims 

 who had been to the 

 Holy L,and. Most of the 

 pectens are ornamented 

 with radiating ribs, but 

 a few are smooth. Some 

 swim freely by flapping 

 their valves, others live 

 permanently attached by 



a byssus. The animal has the mantle free, and frequently bears a row of brightly 

 colored eyes on the margin. The foot is small, the gills are extremely delicate, 



FILE SHELL (Lima} IN ITS NEST (natural size). 



