306 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 
middle piece. For after the formation of the vesicle, head, 
tail, and middle piece are, so far as can be seen, unchanged. 
When the vesicle has reached its full size, the material of 
which its surface is composed seems to wet the sperm head 
very easily. For in the next stage the sperm head is in contact 
with the wall of the vesicle along its whole length, and the 
vesicle has usually assumed a more or less spherical shape. 
Up to this point the transformations were found to take 
place in the same way in all the media employed, but in the 
various Ringer solutions the transformation went no farther 
than this, even when the spermatozoa were left in the solutions 
for forty-eight hours and longer. In the yolk and albumen, 
however, the development toward the formation of a nucleus 
went a little farther. 
After the spermatozoa have been left in contact with the 
culture medium for about eighteen hours, many fairly normal- 
looking nuclei appear, in which the chromatin is all present in 
the shape of discrete particles resting en the nuclear wall, and 
in which no linin, or but very small amounts of it, can be seen. 
It would seem probable that the chromatin in these nuclei 
is derived by a condensation of the uniformly distributed 
chromatin of the previous stage, though it is possible that in a 
certain number of cases the sperm head breaks up into chromatin 
particles without a previous complete solution. 
From these experiments we may conclude that in yolk and 
white of egg the spermatozoon undergoes the transformation 
into a nucleus. We have not noticed any mitosis or aster 
formation and we are, therefore, not yet in a position to state 
that the spermatozoon can undergo mitosis outside the egg. It 
is therefore at present impossible to state that the spermatozoon 
is capable of development into more than a nucleus. 
The question whether or not a spermatozoon can give rise 
to an embryo without an egg cannot yet be answered in the 
affirmative. 
