STUDIES OF FERTILIZATION 517 



has come to be used loosely as practically synonymous with artifi- 

 cial parthenogenesis, as though a salt solution could take the 

 place, and play the role, of the spermatozoon. This it can do 

 obviously only with reference to the initiation of development, 

 which, so far from being the only function of fertilization, is more 

 properly to be regarded as a secondary function, or better a separ- 

 ate phenomenon which is sometimes associated with fertilization, 

 sometimes not. On the one hand we may have initiation of 

 development without fertilization, as in parthenogenesis and all 

 asexual modes of reproduction, and on the other hand the phe- 

 nomenon of fertilization without initiation of development is 

 extremely common, as in the so-called winter eggs of Cladocera, 

 Aphids and Rotifera, where fertilization is followed by a long rest- 

 ing period ; the Protozoa and unicellular algae also offer many in- 

 stances in which fertilization is the immediate prelude to a long 

 resting stage. 



The stud}^ of initiation of development b}^ chemical means has 

 yielded results of prime importance, and the consequent absorp- 

 tion in these problems has been an inhibiting factor in the analysis 

 of other problems of fertilization. Thus, as spermatozoa are not 

 necessary for "chemical fertilization,' the study of their behavior 

 has been largely neglected. The problem of specificity has as a 

 consequence been left almost entirely out of account, for there 

 is no specificity in salts, or even in the blood sera of animals of 

 other phyla; nevertheless specificity in reaction of sexual products 

 is a much more nearly universal phenomenon of fertilization than 

 initiation of development, and it is quite possible that the solu- 

 tion of this problem may furnish a valuable clue in the study of 

 the latter problem. In any event, the time seems ripe for the 

 development of new methods of attack on the fundamental prob- 

 lems of fertilization. The present contribution is a step in this 

 direction. I have taken up the study of the behavior of the sper- 

 matozoa, because it represents, after all, considered in a broad 

 sense, one-half of the problems of fertilization, and it seems prob- 

 able that these small motile cells ma^^ prove better indicators of 

 some of the reactions inxolved in fertilization than the slowly 

 reacting egg. 



