174 A. II. RECxINALD nUl.!,ER. 



VIII. TirE Attachment of Spermatozoa to the Egg. 



As soon as a spermatozoon has penetrated the gelatinous 

 coat it usually becomes fixed b}^ the head to the periphery of 

 the living- egg. Sometimes it executes circles for a while 

 upon the protoplasm, and occasionally even re-enters the 

 jelly and makes its way through this in a radial direction, 

 thus leaving the egg entirely. 



When a great number of spermatozoa are allowed access 

 to an egg which has been some hours in sea- water, so many 

 immediately penetrate and become attached by their heads 

 that they set the egg in rotation. The rotation may be in 

 any direction,^ and often continues for about a miuute, 

 ceasing with the formation of the vitelline membrane. The 

 rate of revolution varies according to the number of sper- 

 matozoa attached to the egg. A rapidly moving egg of 

 Arbacia was observed to make ten revolutions in thirty 

 seconds. The gelatinous coat during rotation scarcely moves 

 at all, the living egg revolving quite independently within it. 

 The spermatozoa often move the egg with such force as to ^ 

 separate it from its gelatinous coat. One then observes that, 

 except for those attached by their heads to the egg, there is 

 no collection of spermatozoa around the latter. This fact is 

 in accordance with the supposition that no chemotactic sub- 

 stance is excreted by the egg. Numerous spermatozoa enter 

 the isolated gelatinous coat. 



The spermatozoon attaches itself to the egg by its most 

 adhesive part, i. c. the tip of the head. The question arises 

 whether the attachment is purely mechanical. It may be 

 that the outer surface of the protoplasm is such as to be 

 best adapted for retaining a spermatozoon by adhesion as 



' For the pggs of the Fucacesc the rotation appears to tx- constantly in a 

 clockwise direction. Thus Farmer and Williams (' Vh\\. Trans. |{oy. Soc.,' 

 vol. 190, 1898, p. 033) state for Ilalidrys " the movement is always in a 

 clockwise direction." 1 have also found this true fur Cystoeyra l)arl)ata. 

 The fact as yet has not been explained. 



