42 Sir Everard Home on the propagation of the 
distinguished by its more internal situation, and its colour, 
which is a shade darker. 
In the month of March, the ova are so large as to be 
distinctly seen in the field of the microscope, and are then 
spherical ; as they increase in size, the membrane to which 
they are attached becomes thickened. In June, they have 
arrived at their full size, and a white fluid like cream is now 
noticed surrounding them. That this is the impregnating 
liquor, is more than rendered probable by the ova dropping, 
or having dropped from their pedicles, and undergone a 
change in their appearance, a vesicle having formed, soon 
after which they leave the ovarium. 
For this purpose a tube becomes visible, which before this 
period could not be detected ; it originates by an opening 
between the two ovaria, which communicates with them both, 
and forms a sheath, in which the intestine is enclosed ; it ter- 
minates externally by an orifice between the lips that sur- 
round the mouth of the oesophagus. This tube is the oviduct, 
which is single. The embryo is found when it enters the 
oviduct, to have already acquired a shell. The young 
begin to leave the ovaria in the end of June ; and at the 
latter part of July none are to be found either in the ovaria 
or oviduct. On the 5th of August oysters are brought to 
market. 
The ovaria, after the spawning has taken place, are not 
visible to the naked eye, but do not become evanescent, since 
in the microscope, fresh ova are seen in the very early part 
of their formation. 
As fishes are what is called in high season while the ovaria 
are full of ova, it was to me not a little extraordinary that 
