480 THE AMERICAN NATURALIST [Vol. LVI 



by the tractive current, and emerges posteriorly in company 

 with numerous large greenish eggs, about which, under the 

 microscope, it can be seen that many sperms are gathered. But 

 no real "cluster-formation" takes place. 



The body juices of the ripe female, whether or not diluted 

 Avith sea water, do not cause agglutination of sperm suspen- 

 sions. But ovarian extracts from {mature) eggs in sea water 

 do induce decided and apparently typical agglutination. So 

 far as I know, sperm-agglutination by ovarian extracts has not 

 previously been seen in molluscs.'' Sea water into which ripe 

 eggs have been shaken from an ovary and the whole allowed to 

 stand for half an hour has a similar agglutinative effect. 



Concerning the significance of the cluster formation, then, 

 these two points seem significant: (1) the absence of such a 

 process in normal fecundation, and (2) its conspicuous occur- 

 rence when sperm, before the real onset of the breeding season, 

 has passed through the ctenidial channels of males or immature 

 females. It could not be discovered whether or not the mature 

 female in a non-spawning interval would cause this cluster pro- 

 duction, because at such times tlie consistent response of a fe- 

 male to an impinging current of sperms was to depress the 

 girdle to tlie substratum, thus cutting off the water current 

 carrying sperms, and, by reducing the volume of the ctenidial 

 channel, violently to expel from below the sperms already ad- 

 mitted. 



These observations do not, of course, permit analysis of the 

 role of egg-substances in fertilization of chiton, but do serve 

 to point the contention that mere evidence of si)erm agglutina- 

 tion (cluster formation) may well have no bearing on such anal- 

 ysis. It is possible that the sperms set free at a period before 

 tiie natural ripening of eggs arc in some degree immature, their 

 surface jierhaps more sticky, or liable to be made so by slight 

 external changes experienced in passing between the gill fila- 

 ments of another individual. 



W. J. Crozier 



