STUDIES OF FERTILIZATION 523 



'12). The tail of the si)(>rnia1ozo<)ii is altaclicd not lo tiiccciitcr 

 of tho middle pi(MM% but on one side. 



The niovenient is of course due to suceessixc heals of Ihe tail 

 ajid it is a very ii^terestiii"- fact that under certain conditions of 

 aggre^'ition the successive beats of the spermatozoa forminjj; an 

 aggregation may l)ecome synchronous, and mider such circum- 

 stances the number of beats approximati^s 120 a iuinutc at 

 temperature of 21°C., if the sperm be fresh. This phenomenon, 

 which I have not yet attempted to anal^-ze in detail, follows after 

 the aggregations of sperm from a fresh suspension have settled on 

 the bottom of the container and begin to spread out of their own 

 weight. Its appearance may be accelerated by gentle agitation 

 of the dish, which tends to spread out the aggregations. Syn- 

 chronous movements appear when the sperm spread out in a kind 

 of membrane from an aggregatetl condition. In such a case the 

 synchronous l)eats spread over the membrane thus formed, like 

 wa\'es of contraction ovei- a ciliated epithelium. In fact, a kind of 

 synthetic ciliated e})itheliuni is then established. The intei-est of 

 the phenomenon in the present connection is that it furnishes a 

 clear demonstration of the successive beats of the tail of the sper- 

 matozoa, which are not readily distinguishable, and certainly 

 cannot be counted, in the case of a single spermatozoon. 



The movements of the spermatozoa are, then, due to succes- 

 sive beats of the tail, which is so placed as to cause rotation in a 

 definite direction. The mo\'ement when freely suspended in 

 water is in a spiral path, but when in contact with a surface 

 the translatory component of the locomotion is almost entirely 

 eliminated. 



The following account of the behavior does not deal directly 

 with individual movements, but always concerns mass-reactions, 

 from which the behavior of the individual spermatozoa may be 

 inferred. 



S. 'Freshness^ 



The spermatozoa are absolutely immotile while they are in 

 the body of the male, but become intensely active when suspended 

 in sea-water. This expresses itself in the formation of aggrega- 

 tions; but, as already noted, aggregations form more slowly after 



