Royal Society. 53 



retained longer, and that when the spermatic fluid has contained 

 many undeveloped cells, and has been preserved in a temperature of 

 51° Fahr., it has fertilized at the end of twenty-four hours. The egg 

 loses its fitness to be impregnated very soon after it is passed into 

 water, usually within the first hour, owing chiefly to the endosmosis 

 and expansion of its enveloj)es. But when retained within the body of 

 the dead frog its vitality is preserved for twenty- four, and sometimes 

 even for forty-eight hours, at a low temperature. He next shows that 

 the results produced by the active vibratile spermatozoa on the dead 

 egg are similar to those which are at first produced on the living one 

 by solution of potass, viz. the yelk becomes shrivelled and con- 

 tracted, and this result also occurs when decomposing spermatic 

 fluid is applied to it. Having repeated the experiments formerly 

 mentioned (Proceedings, p. 83), that the frog's egg may be fecun- 

 dated by application of exceeding minute quantities of spermatozoa 

 by means of the head, and even of the point of a small pin, to 

 almost any part of its surface, he shows that there are some parts 

 of the surface more, and some less, susceptible than others ; and that, 

 in a series of careful experiments made with a view to test this fact, 

 he found that when the egg is placed vertically, with the centre of 

 the white surface uppermost, and the spermatozoa are applied to 

 this part, and not allowed to flow over the sides of the egg, fecun- 

 dation is then but rarely eff^ected ; but that when the centre of the 

 dark surface is uppermost, and the spermatozoon is applied to that 

 part, fecundation of the egg is then almost invariably the result. A 

 fact is also mentioned which is of some value in experiments on 

 artificial impregnation. The chamber which is formed above the 

 yelk in the fecundated egg, as described in the author's former 

 paper, is commenced at the end of the first hour, by the contraction 

 and depression of the upper or dark surface of the yelk ; and thus 

 aff^ords an early proof as to whether or not the egg has been fecun- 

 dated. When no chamber is formed, it is certain that the egg has 

 not been fecundated. But the chamber may be formed, and the yelk 

 not undergo segmentation ; in which case fecundation has been only 

 partial and incomplete. The motion of the spermatozoon in relation 

 to its function is then examined, and the author states that he re- 

 gards this motion as only the visible exponent of a peculiar power 

 in the impregnating agent, and as essential to its function, and that 

 it is associated with the material composition and structure of this 

 body, the degree of procreative efliciency of which, he thinks, is 

 indicated by the degree, or intensity of its motive power ; although 

 he believes that some portion of the substance of the body of the 

 spermatozoon is also communicated to the egg in fecundation. 



The author then shows that having adopted a mode of examining 

 the egg, beneath the microscope, at the time of the spermatozoa 

 being supplied to it, diff'erent from that which he formerly employed, 

 he has been enabled to detect the fact of penetration by the sperma- 

 tozoon into the envelopes, and its arrival at the vitelline membrane, 

 with great facility. Availing himself of the fact previously ascer- 

 tained, that impregnation may be eff'ected by the direct application 

 of the spermatozoon by means of the pin's head or point, he put the 



