98 
THE PEARL OYSTER 
measuring -^ths of an inch across,, while No. 1 measured 
The sole of the foot was nearly white, the upper part was 
mottled light-brown of the same color as the shell of the 
animal, which in this instance was sandy. 
Dr. Kelaart gives the length of the foot of a mature 
oyster as 2 5 inches when distended in use and 1| in rest. 
The breadth of the shell of a mature pearl oyster from hinge 
to contour is, I may add, about 3 or 85 inches. In my 
young oysters the length of the foot and breadth of the shell 
were the same, indicating, quantum valeat, that the foot of 
the young oyster is larger in proportion than that of the old 
oyster, in consonance with greater migration in youth than 
in maturity ; and the young are said on all hands to be more 
active than the old oysters. 
The thinness of the glass tumbler and the excellent light 
greatly favored my observations. 
The persistent striving of these oysters for the surface 
seems to indicate that while oecupjTng the bottom of the sea 
they prefer to be sufficiently raised from it by rock or other 
substance to be free from the wash of sand ; accordingly we 
find they cluster on rocks 4 and 5 feet off the bottom and 
even climb the chain of a buoy. 
The foot, then, indicates the migratory habit of the pearl 
oyster, and especially in youth. "We shall see that the bi/-^sus 
and the shell also point in the same dii-ection and with the 
same limitation. 
We may note, however, before bidding adieu to the foot, 
that it is also used like a hand for directing the point of 
attachment of each thread of the byssiis. 
The Bi/ssus. 
The very presence of a byssus is again another indication 
of a transitory as distinguished from the permanent cemented 
