STUDIES OF FERTILIZATION 583 



by the use of hypertonic sea-water for instance. It therefore 

 seems possible that the two phases of fertihzation may be dis- 

 connected in the case of the spermatozoon also, activated per- 

 haps by different parts of it. On the other hand there is the 

 possibility that fertilization is a continuous process and that 

 the second step cannot proceed if the first be skipped; that the 

 spermatozoon in other words receives some necessary modifi- 

 cation, by union with the fertilizin or other substances experienced 

 in the cortex of the egg. 



The latter point of view seems more probable to me for the 

 following reasons. In the first place I have made some yet 

 unpublished observations in the case of Nereis which show that 

 if the cortical changes be induced by artificial means there is a 

 brief period in which insemination of the eggs may be followed 

 by penetration of the spermatozoon, but without causing cleavage 

 of the egg. Such a result might conceivably be due to a lack of 

 synchrony between the movements of the egg-nucleus and the 

 sperm-nucleus owing to the start given the egg-nucleus by the 

 treatment prior to insemination. This explanation does not 

 seem to me to be entirely reasonable, because, in Nereis, the 

 sperm enters during maturation and has therefore abundance of 

 time to prepare for union with the egg-nucleus. It seems more 

 probable that the egg has lost something which renders the intro- 

 duced sperm inefficacious. As a matter of fact, all the fertilizin 

 is thrown off or neutralized in Nereis during the cortical changes, 

 as I have determined by numerous experiments. Miss Allyn ('12) 

 also determined for Chaetopterus that potassium chloride, which 

 starts parthenogenetic development in this form, "initiates changes 

 which increase with time and which are inimical to normal fer- 

 tilization. They do not prevent the entrance of the sperm into 

 the egg, but they prevent the normal behavior of the sperm in 

 the egg." The cor,tical changes are not very obvious in Chae- 

 topterus, but it is reasonable to suppose by analogy that in initiat- 

 ing parthenogenesis the fertilizin is bound; the sperm entering 

 after this event are relatively inefficacious. 



Dr. G. L. Kite kindly allows me to refer to some yet unpub- 

 Hshed experiments performed last summer in which he injected, 



