194 Mr. Howard Martin on Oysters. 
that either cross- or self-fertilization may take place according 
to circumstances in the same flower, but what perhaps strikes 
us as most remarkable is the dependence of plants and insects 
upon each other, proving that there is a very intimate connection 
between the sciences of Botany and Entomology, and that the 
study of one must to a certain extent involve the study of 
the other. 
126.—Ovysters. 
By Howarp Martin. 
(Read November 19th, 1895.) 
To a superficial observer there does not appear to be anything 
particularly interesting about an oyster, and at first sight he 
appears to be an inanimate lump of gelatinous matter, leading a 
life of motionless monotony. But thisis not so. They begin life 
swimming about in the water, pass through a life threatened by 
many dangers, and are only at last brought to maturity and per- 
fection by constant care and labour. I believe there are forty- 
eight varieties of oysters described in catalogues of bivalves. But 
all the European oysters, except the Portuguese rock oyster, are . 
included in the variety Ostrea edulis, the Portuguese and American 
rock being O. angulata. 
As regards the fish itself, it is contained in an outer skin, 
called the mantle, closed in a kind of hood or pocket at the 
extremity nearest the hinge of the shells, but open at the edge. 
This mantle covers a large gland, in which the eggs are pro- 
duced ; the liver is enclosed in this gland, and the stomach is 
enclosed in the liver. The heart lies in a little cavity near the 
centre and nearest to the flat shell. The oyster breathes through 
four gills within the open edges of the mantle, which are fur- 
nished with cilia, which by a waving motion draw a current of 
water over the gills. The oyster has a mouth furnished with 
four lips, two on each side of the opening, from which the in- 
testinal canal passes through the stomach and out to the open 
edge of the mantle. 
(A series of diagrams illustrating the anatomy of the oyster 
and the growth of spat were shown.) 
It is curious that the adductor muscle shifts its position with 
the growth of the shells, which takes place on the open edges and 
not at the hinge, so as to keep the same position relatively to the 
centre of the shell. 
The oyster is hermaphrodite; its eggs are hatched in the 
mantle, and ejected fully-developed oyster larve or spat—at least 
