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- 

 mencement of the changes, and to be intimately connected with the act of impregna- 

 tion. RUSCONI deprived the ova of the green aquatic frog, ? Rana esculenta, 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-{~." 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 I was not fully aware of its 

 interest and importance, enables me to confirm this observation. I captured 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 ovariurn 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. f Loc. tit., p. 9. + Dissertations, &c., ii. 152, 3. 



MDCCCLI. 2 F 



