276 



The Journal of Heredity 



during the embryonic development or 

 even at a later stage. 



"Evidence for determination by the 

 egg apart from fertilization was drawn 



(1) from the facts of parthenogenesis, 



(2) from sex-limited transmission by the 

 female, and (3) from cases in which 

 two kinds of fertilizable eggs are 

 ]3roduced, which differ from each other 

 in their chromosomes. In all these 

 cases it is certain that, normally at 

 least, male-determining and femnlc- 

 dctermining eggs are produced, and that 

 if the kind of egg is known, the sex can 

 be predicted without reference to the 

 spermatozoon. 



" Similarly, evidence for sex-determin- 

 ation by the spermatozoon is pro\'idcd 

 (1) by the cases in which unfertihzcd 

 eggs yield males, fertilized eggs females, 

 as in the bee; (2) by sex-limited trans- 

 mission by the male, and (3) by the 

 existence of two kinds of spermatozoa 

 differing in respect of their chromo- 

 somes. In each of these three groups 

 the evidence for sex-determination is 

 exactlv comi)arable with the similar 

 determination by the egg in the previous 

 class." 



\ SIMPLE HYPOTHESIS 



If this were the extent of our knowl- 

 edge, we would have fairly clear sailing. 

 "Sex might be regarded as depending 

 on the presence of a greater or less 

 amount of some ' scx-dctcrmining sub- 

 stance' present in the chromosomes, or 

 more correctly, on the physiological 

 condition arising from the interaction 

 of this sub.stance with the substance of 

 the cells. The presence of an additional 

 'dose' of this substance in a cell other- 

 wise similar would alter its metabolism 

 (i. e., general physiological conditi(jn), 

 and since all cells of the body would 

 contain the extra dose, the whole 

 physiology of the body would be affected, 

 and the sex of the animal would be 

 irrevocably determined." 



"So far the problem is relatiwly 

 simple: although nothing is known of 

 the manner of action of the sex-deter- 

 mining factor su])posed to reside in the 

 sex-chromosomes, it can at least be 

 said that in the cases mentioned it is 

 inherited like anv other Mendelian 



character (as was first suggested by 

 Batcson and by Castle), and that 

 individuals which receive it from both 

 I^arcnts would be of one sex, those to 

 which it is transmitted by one parent 

 only, of the other sex. 



"To this scheme, so attractive in its 

 comparative simplicity and its close 

 accord with the facts on which it is 

 based, there are opposed a series of 

 observations, usually derived from spe- 

 cial cases and differing widely in kind 

 among themselves, any one of which 

 might perhajjs be regarded as due to 

 error or to chance, but which, when 

 taken together, make a rather formid- 

 able obstacle to the acceptance of the 

 hy])othesis. They may be grouped 

 under two heads, including ( 1 ) evidence 

 that the egg ma}- influence the sex 

 in cases in which observations on 

 chromosomes indicate that the sex 

 should be determined by the sperma- 

 tozoon; and (2) evidence that the sex 

 may be modified after fertilization by 

 influences acting on the embryo or 

 even later in life." 



These various objections are of such 

 weight, in Dr. Doncastcr's mind, as to 

 make him feel certain "that sex- 

 detcnnination does not depend on an 

 unmodifiable unit, but rather on the 

 reciprocal action between an inherited 

 factor and its surroundings." In the 

 absence of disturbing factors, sex will 

 indeed be determined by the chromo- 

 somes; and "if the difference between 

 the chromo.somcs of the male and 

 female is considerable, it ^^•ill outweigh 

 any other influences which might tend 

 to affect the general result." If the 

 difference is not great, the chromosomes 

 can absolutely determine the sex only 

 under favorable conditions; if other 

 agencies intervene "it becomes possible 

 for an egg which would otherwise have 

 been female to de\-elo]) into a male." 



SEX-DETERMIN.\TION IN .M.\N 



Finally, a few words on the ever- 

 interesting subject of sex-determination 

 in man. From what has been said, it 

 will be fairly obvious that wc are not 

 now in a jjosition even to predict the 

 sex of any child, much less to control it. 

 Hut ihe possibility of e\-entual control 



