192 MR. NEWPORT ON THE IMPREGNATION OF 



that the time is much more extended in the Frog ; that fecundation may take place 

 when the temperature ranges from 53 FAHR. to 59 FAHR. at the expiration of one 

 hour after immersion of the eggs ; that some eggs are fecundated at two, and a 

 very few even at the end of three hours, after which no fecundation takes place. 

 The results obtained by myself both on the Frog and Toad have been most in ac- 

 cordance with those by SPALLANZANI. This is the more worthy of notice from the 

 circumstance that a slight difference between his and mine is readily accounted for 

 by a corresponding slight difference of temperature, which SPALLANZANI, and PRK- 

 VOST and DUMAS, have remarked, and since them also Mr. BELL*, has great in- 

 fluence on the changes of the eggs and young. The temperature at which my test 

 experiments were made, was a little lower even than that at which PREVOST and 

 DUMAS made theirs ; and yet I was not able to find any ova susceptible of fecunda- 

 tion after they had remained from thirty to forty minutes in water. On careful 

 examination of PREVOST and DUMAS' experiments, I think the difference may perhaps 

 be due to a circumstance which seems equally to affect some of SPALLANZANI'S 

 results, namely, the mode in which the impregnating fluid employed was obtained. 

 These authors state that the fluid they employed was expressed from the testicles of 

 the frogs, so that from what we now know of the mode of origin of the sperma- 

 tozoa, this fluid in all probability contained a large proportion of developmental cells 

 that included spermatozoa not fully matured, but which might become liberated in 

 the water at a longer or shorter period. Or, possibly, the fluid added to ova that 

 had been long in the water, had been very recently obtained ; in which case the 

 vigorous spermatozoa might effect the impregnation of ova that had become almost 

 insusceptible through the imbibition of water by their envelopes. I am led to this 

 view by the fact that the jelly-like envelope of the Frog's egg begins to imbibe and 

 expand the instant it is brought into contact with fluid ; and from having ascertained 

 that there is a close relation between the degree of expansion and imbibition of this 

 envelope and the susceptibility of the ovum to become impregnated, and that these 

 conditions are also greatly affected by temperature. The act of expansion of the 

 envelope is an act of endosmose, and possibly this is one of the means by which the 

 impregnating agent is made to exert its influence on the yelk. The yelk is not a 

 passive recipient during the endosrnic action of its coverings, but seems to partici- 

 pate in that action, as I have seen portions of its surface heave and contract within 

 the vitelline membrane during the first hour the egg has remained in water. It may 

 thence be inferred, that if the impregnating stimulus be not supplied quickly, the 

 fitness of the ovum to become impregnated is diminished in proportion as its enve- 

 lopes are expanded. If then it be proved that the spermatozoon is the agent in impreg- 

 nation, but, so far as can be discovered, does not penetrate bodily into the ovum or 

 its envelopes, and yet, as may be shown, must always come into contact with their 

 surface, the more rapidly and to the greater extent this expansion takes place, and 

 removes the efficient body from that which it is in some way destined to affect, the 



* British Reptiles, p. 92. 



