66 SHELL-FISH COMMISSIONERS’ REPORT. [Jan., 
Ostrea Canadensis, or Canadian oyster, abundant about the 
Gulf of St. Lawrence; the Ostrea Borealis, or Northern 
oyster, found along the New England coast; and the Ostrea 
Virginiana, or Southern oyster, crowding Chesapeake Bay 
and neighboring waters. These varieties are found in 
other than their native waters; and when they grow side 
by side, together, their natural differences of form and 
flavor almost disappear. ‘They grow faster and larger than 
the European oyster, Ostrea Hdulis. The valves of the 
former are more expanded and more concave; the fiesh is 
much larger and thicker; the adductor muscle is more 
tender, and the flavor is richer. The demand for the for- 
mer is annually increasing in Europe. The native oysters 
of Connecticut, Ostrea Borealis, are in especial favor. 
The two shelis or valves of the oyster are hinged to- 
gether with an elastic cartilaginous cushion that tends to 
throw them open to a limited extent, ordinarily about a 
fourth of aninch. The tenant is attached to each valve 
solely by means of the adductor muscle, popularly but 
erroneously called “the heart.” In the American oyster 
this muscle has a slighter hold upon the pearly surface of 
the shell than does that of the European species. By 
contracting this muscle the valves are closed, overcoming 
the resistance of the elastic cushion at the hinge. By re- 
laxinge this muscle the elastic cushion is permitted to 
expand, and so it opens the valves. As the oyster grows 
longer the adductor muscle from time to time changes its 
place of union with the shell, slpping, in some unexplain- 
ed way, further towards the nibs, or open ends of the valves, 
thereby securing a better leverage for its special work. 
The successive points of adhesion to the valves can be 
readily detected by the crescent-shaped marks on the pur- 
ple spots in the shell. The operation of the cushioned 
hinge is mechanical; that of the adductor muscle is func- 
tional. When the oyster dies the latter becomes relaxed, 
and the elastic cushion keeps the valves apart. 
The young oyster emerges from the egg with shells par- 
tially formed. He enlarges his shells by expanding his pal- 
liwm, or mantle, which is his outer fleshy covering, beyond 
