196 
cient to affect the mature animal, but that in this case the- 
water continued fresh, or practically so, for too long a period, 
thus killing the oysters by endosmose. 
From the observations of density, then, it may be assumed 
that the density of the water in these localities at least cannot 
fall below 1.01 for any protracted period without destroying 
the oysters. 
Whether the changes in density affect the spatting can only 
be ascertained by continuing the observations for a number 
of seasons, or by direct experiment with the spat artificially 
raised. 
During the summer I have examined, under the microscope, 
374 oysters, of which 212 were females and 162 males, or the 
percentage of females to males was 0.56. 
The oysters were not all examined at the same time, nor 
were they all from the same bed, but the percentage in each 
of the lots examined, twelve in number, does not vary greatly 
from the percentage given above. 
I am of the opinion, therefore, that about 60 per cent, of 
the oysters in a community are females. A larger number of 
observations is, however, desirable. 
In making these examinations I have never seen both ova 
and spermatozoa in the same animal, though I have made 
many careful observations in order to detect the presence of 
either. I have also carefully examined the gills and mantles. 
of a large number, and have never found an embfyo oyster 
within the shell. 
As these observations were made during the spawning sea- 
son, I do not think it possible that the spat, if they are at any 
time contained within the gills or mantle, could have escaped 
my notice. 
The observations as to the sex of the oyster were continued 
late in the season, and though the ova and spermatozoa in a 
number of oysters was in apparently good condition as late 
as the 1st of October, yet those products of generation ap- 
peared in best condition in the largest number of animals dur- 
ing July. 
A considerable disintegration of the eggs was noticed by 
