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SCIENCE 



[N. S. Vol. XXV. No. 636 



ent during the earlier stages of their exist- 

 ence, but that these differences disappear 

 at the moment of fecundation. It has 

 since been shown that the difference in 

 staining reaction of the germ nuclei is 

 probably of secondary significance only, 

 but the view that a primary physiological 

 difference between the germ-nuclei exists, 

 is not necessarily excluded. 



The question has arisen whether we are 

 to deny the old biological conception of 

 a sexually indifferent stage in the life his- 

 tory? It seems to me that this concep- 

 tion is as necessary and fundamental to- 

 day as it ever appeared to be, and that we 

 can not depart from it without involving 

 ourselves in absolutely hopeless theoretical 

 difficulties. Frank R. Lillie 



University of Chicago 



sex determination in relation to fertil- 

 IZATION AND PARTHENOGENESIS 



It is not an easy task to attempt a brief 

 discussion of the relation of sex determina- 

 tion to fertilization and parthenogenesis; 

 for the fact may as well be admitted at the 

 start that we are not yet in a position to 

 make any general statement as to what 

 that relation is, and it is my impression 

 that the subject is not yet ripe for discus- 

 sion. We are not yet, I think, in a posi- 

 tion to conclude with certainty in any 

 single case that fertilization can be con- 

 sidered as a sex-determining factor, not 

 even in the classical case of the bee. Even 

 in cases which at first sight seem clearly to 

 show that fertilization is such a factor, con- 

 sideration will show that we can not, or at 

 any rate have not, shut out the possibility 

 that fertilization may be determined by sex 

 rather than the reverse. There is the same 

 uncertainty regarding the relation of sex 

 production to parthenogenesis. There is 

 no constant relation between these two 

 processes, for the parthenogenetie eggs of 

 a single individual may in the same species 



produce females only, males only, or both 

 males and females. Both fertilization and 

 parthenogenesis, in fact, present us with a 

 series of relations to sex production in 

 which the common factor, if there be such 

 a factor, still eludes us. 



There are two primary data which, I 

 think, must be taken as our point of de- 

 parture in any attempt to discuss these 

 problems. The first is the long-known fact 

 that in a few cases, of which the best known 

 are those of Dmophilus apatris and Eyda- 

 tina senta, the eggs are visibly distinguish- 

 able by their size as males and females, 

 before fertilization or even maturation. 

 Neither fertilization nor maturation, ac- 

 cordingly, can here be a sex-determining 

 factor. We only know, if the results of 

 Maupas and Nussbaum on Hydatina and 

 the more recent ones of von Malsen on 

 Dinophilus be well founded, that in these 

 cases the ratio between male eggs and fe- 

 male eggs may be modified by conditions of 

 temperature, or nutrition, or both, that 

 affect the mother before the eggs are laid; 

 but the true interpretation of this is still 

 very far from clear. The second primary 

 datum is that in many insects, and prob- 

 ably in many other air-breathing arthro- 

 pods, the spermatozoa are predestined in 

 the constitution of their nuclei, as males 

 and females, or better, male-producing and 

 female-producing forms, in equal numbers. 

 Here, however, our actual knowledge ends, 

 so far as fertilization is concerned. We do 

 not know in any single case whether the 

 predestination exists in both eggs and 

 spermatozoa in the same species. Until we 

 can be sure on this point it is almost idle to 

 speculate on the subject; for if such a 

 double predestination exists there must ob- 

 viously be a selective fertilization, such that 

 each form of egg is fertilized by the appro- 

 priate form of spermatozoon; and if this 

 be so, sex is not determined by fertilization, 

 but fertilization by sex. Until this ques- 



