AND ON THE DIRECT AGENCY OF THE SPERMATOZOON. 273 



constant observation beneath the microscope, rather than to that to which the 

 undisturbed mass of eggs was exposed. The temperature of the atmosphere of the 

 room at the time the eggs were deposited was 54 FAHR., but it gradually sunk to 

 51'5 FAHR., and the water in which the eggs were contained to 50 FAHR. at the time 

 when segmentation commenced, at the end of six hours and thirty Jive minutes. In 

 the most submerged it did not take place until six hours and forty-Jive minutes had 

 elapsed. 



In nearly the whole of the eggs of this mass which had been fecundated by the 

 natural union of the sexes, I was struck with the fact that the quantity of sperma- 

 tozoa which had penetrated into every part of their envelopes was very considerable. 

 Very many of these had arrived at, and were sticking by their larger end into the 

 vitellary membrane, from which they projected like spines from the head of a thistle ; 

 while there were many others which had not arrived at this part, their power of 

 penetration being exhausted, and their progress inwards being arrested before they 

 had passed more than half-way through the outer gelatinous coverings. Others, 

 again, had penetrated to scarcely more than their own length into them, while a still 

 greater number were simply in contact with, and adhering to the external surface. 



When segmentation took place in these fully impregnated eggs, their yelks seemed 

 to contract more powerfully, and the clear space, or respiratory chamber, formed in 

 each became much larger than in others from the same mass in which but a few 

 spermatozoa were detected ; so that the inference deducible from the fact seemed to 

 be, that a plurality of spermatozoa is necessary for the full impregnation of the egg, 

 and the production of the robust and healthy embryo although simple fecundation 

 may result from the influence of only a very few spermatozoa, especially when such 

 influence is aided by a considerable increase in the temperature of the surrounding 

 medium. 



Mode of Penetration by the Spermatozoon. The preceding observations on natu- 

 rally fecundated eggs were so decisive of the fact of penetration by the spermatozoa 

 into at least the envelopes of the egg, and of the arrival at, and partial imbedment of 

 these bodies in the vitellary membrane, that it seemed desirable to make further 

 observations, by the artificial method, with a view to ascertain more directly the 

 mode and circumstances of their entry ; and these it was hoped might be learned 

 through the facility with which the egg may be impregnated by direct application 

 of spermatozoa to almost any part of its surface. Accordingly, on the following 

 day, I placed an egg in a glass cell, beneath the microscope, and quickly afterwards 

 applied to one side of it, by means of a pin-head, a quantity of spermatic fluid, ob- 

 tained from the male only a few minutes before, and immediately filled the cell with 

 water, and commenced the observation. The fluid was applied four times to the 

 same part of the egg, the pin-head being loaded for each application, in order that a 

 full sufficiency of spermatozoa might be furnished, before the water was added. The 

 temperature of the room at the time of the experiment had been intentionally raised 



