44 Sir Everard Home on the propagation of the 
may be enabled to consider them, which is no part of the 
present enquiry. - 
The stomach and intestine of the oyster I have upon ano- 
ther occasion considered and delineated, and laid before the 
Society. 
The heart has a near resemblance to that of the teredines, 
having two auricles and one ventricle. 
On the mode of breeding of the fresh-water muscle. 
In this bivalve, the ovaria in their situation and appearance 
are the same as in the oyster. The ova arrive apparently at 
the same size before they are impregnated, which in them 
also takes place in the ovaria. 
The ova, while attached by their pedicles to the membrane 
of the ovarium, have an appearance only to be distinguished 
from the structure of the liver by the difference of colour. 
About the 1 oth of August the ova are completely formed 
in the ovaria, and are detected about the 20th of the same 
month passing into the oviduct, which is a curiously trellised 
structure situated between the membranes that compose the 
bronchiae ; and about the 12th of September they have all 
arrived there. 
That impregnation has preceded this change of situation is 
evident from the ovum having been formed into a vesicle, 
through the coats of which vesicle, very soon after it has 
been retained there, the embryo is distinctly seen surrounded 
by a fluid, opening and shutting the incipient shells for the 
aeration, and probably the nourishment of the foetus in this 
stage of its growth. 
While in this situation, many of the young were seen 
