786 



SCIENCE 



[N. S. Vol. XXVII. No. 698 



tte gametes of the male there is no coupling; 



(3) that in fertilization union can only take 

 place between gametes bearing opposite sexes; 



(4) that dominance attaches to the sex brought 

 in by the ovum ; the observed results would be 

 produced. 



On reexamination of the case we have found 

 a much simpler and, as we think, more prob- 

 able account of the phenomena. Two assump- 

 tions only are needed: (1) that one female is 

 heterozygous for sex, femaleness being dom- 

 inant, and the male a homozygous recessive; 

 (2) that when in F^ the two dominants, fe- 

 maleness and the grossulariaia factor coexist, 

 there is a repulsion between them, such that 

 each gamete takes one or other of these two 

 factors, not both. Such mutual repulsion of 

 two dominants has already been shown to 

 occur in the sweet pea when a plant is hetero- 

 zygous for the upright standard and for the 

 blue factor, constituting what must be re- 

 garded as a spurious allelomorphism between 

 them.^ 



The whole series of facts is then consistently 

 represented as follows, D and R representing 

 / the presence and absence of the grossulariaia 

 factor : 



1. lad. 9 X gross. $ 



BE 5^ 



DD ^'^^ 



F, 



gross. $ 



gross. 9 

 DR 9^ 



2. F, gross. 9 X Fj gross. $ 



composition 



gametes 



DR 9^ 

 IR 9 





2 gross. $ 

 DR ^•^^ 

 DD J'3' 



1 gross. 9 

 DR 9^ 



1 lad. 9 

 RR 9^^ 



3. lact. 9 X Fi gross. $ 

 RR 9 ^^ Dn $$ 



1 gross. $ 1 gross. 9 1 '«''*• S 1 tec(. 9 



TiR S $ DE 9 ^ RR ^ ^' RR 9 (? 



' Science, N. S., XXVI., p. €55. 



4. Fi gross. 9 X ^<- <? 



DR 9^ 



RR ^^ 



gross. $ 



lact. 9 



RR 9^" 



The numbers originally obtained were very 

 wild and irregular, but on repeating the ex- 

 periments Doncaster got results which are 

 numerically very close to expectation.' 



Attention is drawn to this case as illustra- 

 ting the great value of evidence respecting 

 dissimilarity in reciprocal crosses for the 

 elucidation of the problem of sex-heredity. 

 We have long been engaged on a more com- 

 plex case of this kind, the heredity of the 

 black pigmentation of the Silky fowl, in its 

 crosses with brown Leghorns and other fowls 

 with light shanks. The facts there also point 

 very clearly to a similar solution, but it may 

 be some years before the evidence is com- 

 plete. 



On general grounds it seems to us probable 

 that one and not both sexes of the same organ- 

 ism will be shown to be heterozygous for sex, 

 and that the approximately equal output of 

 the two sexes in ordinary cases is a conse- 

 quence of this. Correns" has lately shown 

 that his experiments with Bryonia suggest 

 that in that plant it is the male which is 

 heterozygous. Eusso' from his experiments 



'Nature, 1807, LXXVI., p. 248. 



' Bestimmung und Vereriung des Qesohlechtes, 

 Bomtraeger, 1907. 



* Atti Ac. Lincei, 1907. Heape (Proc. Roy. 8oc., 

 Vol. 76, B, 1905) described in the rabbit processes 

 by which ovarian ova frequently degenerate, ap- 

 parently as a normal occurrence. Mr. Heape very 

 kindly gave us an opportunity of examining his 

 preparations, and it was impossible to avoid being 

 impressed with the general resemblance which 

 such degenerating ova bore to those which Russo 

 regards as destined to become males. Conse- 

 quently before that view of their nature is 

 adopted, the relation of the so-called " male " 

 ova to the degenerating ova will need very care- 

 ful study; for it seems as yet not unlikely that 

 those differences which Russo has taken to indi- 

 cate maleness may prove to be due to incipient 

 degeneration. Also as regards the important ques- 

 tion of the alleged effect of lecithin in increasing 



