54 Royal Society. 



fact of penetration to a very positive test beneath the microscope, 

 and found that the spermatozoon always penetrates at the parts to 

 which it is applied, and at no other part of the egg, and that a short 

 time afterwards it may be detected striking into the vitelline mem- 

 brane, by its thicker or body portion, in a line with the point at 

 which it has entered, and the centre of the yelk, and that he has 

 usually found eggs so penetrated to have been fertilized and produce 

 embryos. Further, that eggs in which no spermatozoa have been 

 seen in contact with the yelk membrane, have usually been un- 

 fruitful, although numerous spermatozoa have been observed on 

 their surface. During his experiments the author had an oppor- 

 tunity of examining some eggs which had been impregnated by the 

 natural concurrence of the sexes, and then found that these most 

 fully confirmed the results obtained by artificial impregnation. 

 Spermatozoa were observed sticking into the vitelline membrane for 

 many hours after the time at which the egg must have been fecun- 

 dated ; which the author believes must be within the first half-hour, 

 and perhaps within the first few minutes ; as he has sometimes found 

 spermatozoa close to the vitelline membrane within one minute after 

 they had been supplied to the egg. The spermatozoon invariably 

 enters the egg with its thicker or body portion foremost, and passes 

 onwards with a direct but slightly serpentine motion, in a centripetal 

 direction to the vitelline membrane. A large proportion of the 

 spermatozoa never enter the envelopes of the egg, if they happen to 

 come into contact with them laterally, as is frequently the case ; they 

 then merely adhere to the surface, but do not fecundate. The 

 greatest number penetrate when supplied to the egg within a few 

 seconds after removal from the male body, and of the eggs from the 

 body of the female. Some experiments are then detailed which the 

 author states arose out of a communication made to him by Mr. 

 Busk, F.R.S. The spermatozoa were narcotized by exposure for 

 eight or ten minutes to the vapour of chloroform, and it was then 

 found that when in this state, while perfectly motionless, as when 

 dead, they did not impregnate. These experiments, in connection 

 with others, seemed to show that the entrance of the spermatozoon 

 into the egg is not the result of an endosmic action of the envelopes, 

 but is that of the operation of a distinct power in the spermatozoon. 

 The nature of the influence of the spermatozoon is then examined. 

 The author has endeavoured to put this to the test of experiment, 

 first, by immersion of eggs, both before, and at the period of fecun- 

 dation, and during the segmentation of the yelk, in solutions of 

 potass ; and next, by reducing the bodies of recently- obtained and 

 perfectly active spermatozoa, to a fluid state, by trituration in a 

 glass mortar, prepared for the purpose, and then applying the ma- 

 terials so obtained to the egg immediately it is expelled from the 

 female, and before it has been in contact with water ; and conse- 

 quently at the time it is most susceptible of the fecundatory influence. 

 The experiments by immersion in potass solution showed that the 

 endosmic action of the egg envelopes is exceedingly rapid, as decom- 

 position of the yelk was commenced in some within three minutes of 

 the application of the solution. In very weak solution the result was 



