FERTILIZATION REACTION IN ARBACIA PUNCTULATA. 275 



Table VIII. 



The above table shows the series of metals as established for both membrane 

 and cleavage inhibition in Arbacia. With the exception of HgCh they are in the 

 order of increasing concentration. 



concentrations by the addition of egg sea-water, thus demon- 

 strating that the action is not primarily on the sperm before 

 their interaction with the female gametes. 



V. Discussion. 



There are three periods definable in Arbacia from the moment 

 of insemination up to the first cleavage. The first involves the 

 behavior of the spermatozoon alone and includes its activation, 

 migration to the egg, and its agglutination to the egg. The 

 second involves the reaction of both egg and sperm, and lasts 

 from the end of the latent period to the completion of the cortical 

 activation of the egg. It can, of course, be subdivided. The 

 third is concerned with the rotation of the sperm head within the 

 egg cytoplasm, and the migration of the egg nucleus. In other 

 words, it is the preparation for the union of the germ nuclei and 

 the preparation for cleavage. A latent period comes between 

 the time of the agglutination of the sperm to the egg and the 

 initial events of cortical activation, as described by Lillie ('21). 

 It belongs to the first period described rather than to the second. 



The differentiation between the first and second periods is 

 very markedly emphasized by the foregoing experiments. When 

 eggs are placed in solutions indicated in the text as membrane- 

 inhibitory, and immediately inseminated, the sperm are seen to 



