48 Our Food Mollusks 



ductor muscle also appears. Subsequently the foot and 

 anterior adductor degenerate and completely disappear. 



During the formation of the shell the small oysters 

 leave the surface of the water and continue for some time 

 to swim at lower levels. About the sixth or seventh 

 day after development begins, they settle to the bottom, 

 and, if fortunate enough to come in contact with a hard, 

 clean surface, attach themselves by a sticky secretion 

 of the mantle. In the figure, XII represents such a re- 

 cently attached oyster, and shows the finger-like rudi- 

 ments of the inner gill, which is the first of these organs 

 to form. The velum with its cilia, having now become 

 useless, soon disappears. 



The early development of two or three others of our 

 edible bivalves has now been studied, and it appears that 

 the succession of changes in each is very much like that 

 of the oyster, as would be expected. But because of 

 differences in the manner of living in adults of different 

 species, we find diversities of structure appearing soon 

 after the swimming stage. The details of the early life 

 of some of these forms are not yet known, but many ob- 

 servations have been made on the growth and habits of 

 the attached oyster, the small soft clam, and the young 

 scallop, and these will subsequently be mentioned. 



