Sexual Characteristics of Oysters. 47 
rent, differing as greatly in this respect as do the eggs in size 
and details of construction, as shown by the measurements 
which I have given. It must not be forgotten, however, that 
the material from which I prepared my sections was received 
from Europe in January and March, when it is to be supposed 
that the reproductive organs were not yet fully developed, and 
that consequently the dimensions of the ovarian ova as found 
by me are rather to be considered as being below than above 
their true ones when fully developed at the height of the 
spawning-season. 
It is a very remarkable fact that one finds individual speci- 
mens of oysters in which the reproductive organs have under- 
gone total atrophy or wasting-away at the completion of the 
spawning-season. Hxamining sections through the body-mass 
of spawn-spent oysters taken from their native waters in 
August last, I find that the whole of the connective tissue 
subjacent to the mantle, and between the latter and the liver, 
especially over the sides of the body-mass, has disappeared, 
together with all traces of the reproductive organs, including 
the superticial branches of the efferent ducts. At the first 
bend of the intestine there is still some of the connective tissue 
remaining; but even here and in the mantle it has changed 
its character entirely, and become very spongy and areolar, 
instead of solid and composed of large vesicular cells such as 
are met with when the animal is in a better condition of flesh. 
In fact, it appears as if this mesenchymal or connective-tissue 
substance had been used up and converted into reproductive 
bodies (generative products) in the case of the spawn-spent 
and extremely emaciated individuals. In sections of indivi- 
duals in various conditions from that in which the rudimentary 
netwcrk of generative tubules has just appeared in the con- 
nective tissue, on up to those in which the reproductive tissues 
are enormously developed in bulk and proportion to the mass 
of the remaining structures, there is a perfect gradation from 
their complete absence to their full development. This 
would appear to be very strong evidence in support of the 
theory that the reproductive follicles, or tubules, are developed 
anew each season directly from the specialization of certain 
strings or strands of connective-tissue cells. 
Many animals manifest a periodic development of the glan- 
dular portions of the reproductive organs; but I know of no 
form in which there is any such presumptive evidence that 
these organs are annually regenerated and finally altogether 
aborted as seems to be the case with the oyster. ‘Together 
with the changes here described, the most remarkable changes 
in the solidity and consistence of the animal take place. The 
