5O WYMAX REED GREEX. 



| 



factorily in all of its phases. Although very creditable work 

 been done by Chambers ('13) on spermatogenesis in Sinio- 



phalus, and by Weismann and a host of others on the natural 

 history, oogenesis, fertilization, etc., of the Daphnians in general, 

 there is still urgent need of more data. Much time and effort 

 have been expended by the writer in the attempt 'to perfect a 

 technique which would be adequate to the cytological problems. 

 Considerable progress has been made with this phase of the 

 work yet the study is far from completion. The present paper 

 will be devoted to some problems naturally arising in the course 

 of such studies, which should be solved before or at least in 

 coordination with the cytological problems, else the latter 

 Avould lose much of their significance. 



Among such problems are the following: the normal general 

 life cycle must be known; whether this may not be modified by 

 altering the external conditions and if so, to what extent and 

 how ; whether the species may not express itself in all of its forms 

 under each of several sets of conditions, or if there are certain 

 environmental factors which bear special relations to certain 

 forms; whether the failure to produce sexual forms during the 

 parthenogenetic phase is due to a deficiency in the environmental 

 complex or to internal conditions such as age or is dependent 

 simply upon the general rate of metabolism; the normal propor- 

 tions of males and females; the ratio of sexual 1 to asexual fe- 

 males, the sequence of broods; the cause of senescence of the 

 cultures; the cause of the appearance of the ephippial eggs; 

 the time in the ontogeny at which they appear; the precise 

 function of these eggs, i.e., whether the importance of the ephip- 

 pial egg is centered in the egg as a means of tiding the species 

 over unfavorable seasons or periods, or in the stem mother devel- 

 oping from it; the relation of the males to the production and 

 development of the ephippial eggs; the normal length of the 

 latent period; if it be of definite duration; whether it can be 

 shortened and if so, how; whether the offspring of a stem nioiher 



1 By the term "sexual female" in this paper we designate those females pro- 

 ducing series of ephippial eggs which require fertilization; by "asexual female" 

 those which reproduce only parthenogenetically. All so-called sexual females 

 are destined to pass from theii sexual phase into the parthenogenetic phase and 

 so remain. 



