Self-Ferttlization Induced by Artificial Means. 171 



be one of the factors to be taken into consideration, but it is not, 

 I think, the whole explanation. My reasons for regarding this 

 view as insufficient are the following: It was found that sperm 

 that appeared to be very little active was sometimes capable of 

 cross-fertilizing the eggs of another individual. Possibly this 

 may be due to somewhat greater activity induced by something 

 secreted by the eggs of the other individual, yet on the whole I 

 can not claim that direct obsei-vation gave any convincing evi- 

 dence in favour of this assumption. More significant are the 

 results of the experiment of mixing eggs from two Individuals, 

 and subsequently fertilizing them with the sperm from one of. 

 the Individuals. Half only of the eggs segmented, presumably 

 those cross-fertilized. If some substance that makes the sperm 

 active were really thrown out by the eggs, then we should expect 

 that all the eggs would have been fertilized, unless indeed the se- 

 cretion loses its power a short distance from the surface of the 

 egg that secretes it; but this does not seem to be a probable Inter- 

 pretation. 



A different point of view Is that the egg secretes some sub- 

 stance that attracts the spermatozoa. On this view we must 

 suppose that the substance secreted by the egg of Ciona has no 

 attraction for the spermatozoa of the same individual. 



The little evidence that I have to' offer, based on experiments 

 with ascidians. Is not favorable to this idea, that the cross-fertiliza- 

 tion is due to some attractive substance secreted by the egg. In 

 the species that I have examined there is no such marked 

 accumulation of spermatozoa around the eggs as is seen in many 

 other animals, and nothing in the behaviour of the cross- and self- 

 fertilized egg to suggest that the difference in the results is due 

 to an attraction in the one case, and to the absence of an attraction 

 In the other. In other forms where there is a better opportunity 

 for examining this question the most recent observations go to 

 show, as has been pointed out in detail above, that there Is no suf- 

 ficient evidence for the view that the egg attracts the spermato- 

 zoon. 



Conversely, it may be supposed that the egg secretes some sub- 

 stance that repels the spermatozoa of the same individual. I 



