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 hy 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 
