•eleus. The disappearance of the large chamber by a sudden 
contraction, and the diffusion of its contents through radiat- 
ing channels, are phenomena which are as unmistakable as the 
somewhat similar changes of the contractile vacuole of an 
infusorian, although, like the latter, they are somewhat diffi- 
cult to discover, and can only be seen by keeping the egg 
under constant observation. 
In some instances, I was able to actually observe the disap- 
pearance of the germinative vesicle of the oyster egg. In 
many Lamellibranchs this body has considerable elasticity, 
and in Anodonta it may be forced by pressure through a small 
fissure in the ruptured egg-shell, and it will regain its original 
shape and size after it has escaped from the egg. This is not 
the case in the oyster, and in the ripe egg the vesicle seems to 
be almost as fluid as water, and cannot be pressed out of the 
yolk. Like all the changes in the oyster egg, the disappear- 
ance of the germinative vesicle takes place with great rapid- 
ity, and the manner of disappearance is identical with that 
which I have just described in the case of the segmentation nu- 
cleus. It becomes irregular ; radiating channels run off from 
it into the yolk ; the central chamber vanishes, and the chan- 
nels are visible for an instant longer, and then disappear. 
The yolk is so opaque that I was not able to see that any part 
of the vesicle was left behind as a pronucleus, but this is pro- 
bably the case. 
It is useless to speculate at present upon the significance of 
these highly suggestive changes, but they certainly show that 
we may hope for very interesting results from the minute his- 
tological study of the eggs of marine Lamellibranchs. 
In this connection, I may call attention to a point in the 
history of the “Auerbach’s figures.” It is not generaly known 
that these were first figured by Carus, more than fifty years 
ago, in the egg of a Lamellibranch. His figures of the seg- 
menting egg of Unio (Neue Untersuchungen iiber die Ent- 
wickelungsgeschichte unserer Flussmuschel. Yon Dr. J. G. 
Carus. Nova Acta, 1832, 8, 1), show these structures about 
as they are represented by Flemming, but he regards them 
