KARYOKINESIS AND ITS RELATION TO FERTILIZATION. 285 
At this point the egg-membrane, which elsewhere covers the 
disc, has a corresponding aperture. The anterior protoplasmic 
naked end of the spermatozoon fixes itself to the “ bouchon 
d’impregnation ” projecting through the micropyle, fuses with 
it, and is then, by its retraction, drawn into the interior of 
the egg. Whilst its hinder pointed end projects through the 
micropyle, the membrane of the spermatozoon fuses with the 
egg-membranes, withdraws itself from the spermatozoon, and 
thus closes the mycropyle, and forms a barrier against the 
entrance of any more spermatozoa. In six cases out of the many 
thousands studied by E. van Beneden, two spermatozoa entered ; 
these were probably glued to one another by both being fixed 
to the “ bouchon d’impregnation.” More than two were never 
found inthe egg. The micropyle always corresponds with one 
of the ends of the organic axis of the egg. 
I will here interpolate that O. Zacharias in Hirschberg 
(210), who last year studied anew the process of fertilization in 
Ascaris megalocephala, was unable to find any such 
definite micropyle, either in A. megalocephala or in A. 
sulla. He therefore believes that the spermatozoon enters at 
any spot, and ascribes to it the power of dissolving the egg- 
membrane. Carnoy, too, asserted this previously (48), and 
van Gehuchten confirms it (77). It is under these circum- 
stances very difficult to explain why as a rule only one sper- 
matozoon finds its way into the egg. 
From the moment of the fixation of the spermatozoon to 
the “bouchon d’impregnation,” it appears more strongly re- 
fractive, and will, as also will its protoplasmic portion, take 
stains very much more strongly. ‘This, as E. van Beneden 
maintains, is an excellent way of distinguishing the penetrating 
from the merely adherent spermatozoa. 
In order not to interrupt the description of the changes 
in the maturation of the male element, I will now trace it up 
to the act of copulation, remarking again that the eme- 
bedded spermatozoon undergoes no noteworthy change until 
the two directive corpuscles are budded off by the germinal 
vesicle. 
