174 T. H. Morgan. 



stain. I mention these points because they might easily lead one 

 after only a casual examination to conclude that spermatozoa 

 enter the eggs. My best results have been obtained by drawing 

 out the iron haematoxylin until the protoplasm has lost all of its 

 color, or better still by using the Delafield stain, and also thor- 

 oughly extracting the color from the protoplasm. 



Although I have examined a large number of preparations I 

 have not seen a single definite case without ether in which a 

 spermatozoon has entered the egg of the same individual. Diffi- 

 cult as it admittedly is to be absolutely certain on this point, yet if 

 the spermatozoa had entered and had begun to enlarge I feel 

 certain that I should have detected their presence. That un- 

 developed sperm-heads may be present I must admit as a pos- 

 sibility, but I have not detected them, and believe that I should 

 have been able to do so were they present. It is also a point of 

 some importance that I have not found any spermatozoa within 

 the egg membrane, although quantities of them may lie outside. 



There is a further point in this connection, the importance of 

 which I did not appreciate until I had closed the experimental 

 part of my work. In the eggs of many animals a change takes 

 place In the egg, after the penetration of one spermatozoon, of 

 such a sort that the entrance of more spermatozoa is prevented, 

 I have found In Ciona that, after the sperm has stood with the 

 eggs of the same individual and has failed to fertilize them, these 

 eggs could still be readily fertilized by spermatozoa from another 

 individual. If a spermatozoon of the same individual really 

 enters the egg it does not In consequence bring about such a change 

 in the egg that other spermatozoa can not enter, and therefore 

 many spermatozoa of the same Individual from which the eggs 

 were taken should be expected to gain entrance, but I am quite 

 certain that this, at least, does not occur. From this consideration 

 also It may be Inferred that the spermatozoa do not normally pene- 

 trate the eggs of the same individual. 



In the light of these observations it seems probable that whenever 

 a spermatozoon enters the egg, the egg begins to develop regard- 

 less of whether the spermatozoon comes from the same or from 

 another Individual. The ether must therefore induce a change 



