THE OVUM IN THE AMPHIBIA. 
217 
the albuminous investment of the ovum of the Rabbit. I cannot, with Rusconi*, 
regard this envelope of the Frog’s egg as being merely a mechanical protection 
during the process of development. It is formed of cells with distinct nuclei, and 
from what I shall presently mention, seems to be essential to the ovum at the com- 
menpement of the changes, and to be intimately connected with the act of impregna- 
tion. Rusconi deprived the ova of the green aquatic frog, ? Rana esculenia, of their 
gelatinous envelopes at a period subsequent to impregnation, and found that they 
passed through their changes as well as when covered by them ; and he thence con- 
cluded that the envelope is of no use further than to protect the egg from the injury 
it might receive through mechanical disturbance, ‘‘des petits chocs qui pourroient 
nuire a son developpement-f'.” Certainly it affords this protection to the germ, but 
to conclude that this is its sole office appears to be somewhat premature. I have 
found that it is almost impossible to remove this envelope from the Frog’s egg at 
the moment of deposition, or even during the first few minutes after submersion, 
and before it has become expanded by imbibition of fluid ; although it may be removed 
without much difficulty from the egg of the Newt, the yelk of which, in the vitelline 
membrane, lies free and unattached in its interior. But some time after the expan- 
sion has taken place I have myself found that the frog’s egg may be deprived of 
a large portion of this covering, and yet produce an embryo equally well as if it 
had remained protected. On the other hand, one most important function of this 
investment seems to be indicated in the following facts. Spallanzani found that 
ova of the Frog deprived of their envelopes before contact with the male influence, 
were not impregnated ; and further, that ova taken directly from the ovaria, are not 
susceptible of impregnation^. 
A remarkable fact which I noticed, at a time when 1 was not fully aware ol its 
interest and importance, enables me to confirm this observation. I captui ed a pair 
of frogs, the female of which, a short time after they were in my possession, had a 
large hernia formed by a protrusion of part of the great oviduct through an acci- 
dental wound in the posterior part of the right side of the body, and in consequence 
of which she was unable to deposit her ova. This wound had been received before 
the union of the sexes, but the hernia was formed afterwards, during the passing of 
the ova from the ovaria. The result of this was, that when some of the ova had 
passed into that part of the duct which protruded through the wound, the sac formed 
by it was constricted, and became so enlarged by the expansion of the egg-envelopes, 
that the remainder of the ova were prevented from entering it. On opening the ab- 
domen of the frog after death, I found that a very large proportion of the ova which 
had left the ovarium on that side of the body, were lying in the cavity of the perito- 
naeum, among the viscera, being entirely prevented from entering the duct, which 
was filled throughout its whole extent, to its very orifice, with eggs which had already 
entered, and were prevented from passing on. On the left side of the body the ova had 
* Loc. cit., p. 8. t Loc. cit., p. 9. + Dissertations, &c., ii. 152, 3. 
2 F 
MDCCCLI. 
