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 on 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. 



