60 



SCIENCE 



[N. S. Vol. LII. No. 1333 



Drosophila simulans by the action of a 

 mutant gene. He concludes with the remark : 

 It has been assumed by Goldsehmidt, Hertwig, 

 Banta, and others working with intersexes that in 

 their animals the normal sex- determining mechan- 

 ism itself was failing to function as usual. The 

 present example shows that such an assumption 

 can not be accepted without proof.i 



May I be allowed to point out some very 

 important distinctions between this present 

 example and the best worked-out of the 

 others, namely Goldschmidt's intersexual 

 moths (Lymantria). (1) Sturtevant's iuter- 

 sexual Drosophila are all females. Gold- 

 sehmidt has obtained intersexes in both sexes. 



(2) The gonads in Sturtevant's example are 

 described as "minute, if present." In 

 Lymantria, instead of such marked reduction 

 occurring, the gonad is transformed, partly or 

 wholly, into that typical of the other sex. 



(3) Most important of all, Sturtevant's flies 

 appear to be all of one type or grade of inter- 

 sexuality. Goldschmidt's moth intersexes, 

 both male and female, form a continuous 

 series from normality to complete sex-reversal. 



(4) Goldschmidt's analysis of his material 

 has shown that the Lymantria intersexes are 

 zygotes which have started development as 

 individuals of one sex, but at a given point 

 have been switched over to continue as indi- 

 viduals of the other sex. The degree of inter- 

 sexuality depends on the point of time in 

 development at which the change occurs. It 

 is essential to have an analysis of the 

 Drosophila case from this point of vew, be- 

 fore further comparison is profitable. (5) 

 When a highly intersexual female Lymantria 

 which is functional as a male is mated with a 

 normal female, the sex-ratio in the resulting 

 broods is what would be expected if both 

 parents were of Z W chromosome constitu- 

 tion; the same is true when, instead of high- 

 grade intersexes, such individuals of all male 

 broods as must be supposed to be transformed 

 females are bred from. 



With these differences between the inter- 

 sexuality of Drosophila and that of Lymantria, 



1 To this list should be added Harrison, Jour. 

 Genetics, 9, 1919, p. 1. 



we can not be sure that the two are quite com- 

 parable, or due to the same set of causes. In 

 conclusion, it may be said that the Columbia 

 School itself has made it exceedingly probable 

 that the function of the sex genes is normally 

 to initiate one series when present in two 

 do&es; the one series of reactions allowing of 

 the appearance of the structures and instincts 

 of one sex, the other of those of the other sex. 

 If this is so, then there is theoretically nothing 

 whatever against the possibility of these series 

 of reactions, and the physiological states to 

 which they give rise being altered, (1) by the 

 mutation of indei)endent genes (as appears 

 undoubtedly to be the case in D. simulans) ; 

 (II) by an alteration in the balance between 

 the sex-genes and other factors influencing 

 development, (as would seem more than prob- 

 able in Lymantria) ; or, (III) by external 

 agencies (as apparently in Hertwig's and 

 Kuschakewitsch's experiments on frogs and 

 Miss King's on toads). The burden of proof, 

 in the present state of our knowledge, lies 

 even more on the upholders of gene-produced 

 intersexuality than on the upholders of the 

 balance theory, but quite possibly both are 

 right. 



Julian S. Huxley 

 New College, Oxford, 

 May 1, 1920 



THE ORIGIN OF OIL 



A. W. McCoy has published in Journ. Geol. 

 XXVn. (1919), pp. 252-262, evidence that 

 crushing oil shale converts some of the solid 

 organic matter into oil. The conditions of 

 the experiment seem to preclude any chance 

 for much general heating of the mass of 

 shale used. 



Can some mathematical physicist tell us 

 whether a strain or shear would cause a high 

 temporary temperature at the point of rup- 

 ttire? The heat would be absorbed by the 

 adjacent rock and would not greatly increase 

 the temperature of the whole mass, unless 

 the quantity of heat were large. Yet the 

 temperature at some points might le high 

 enough for a very short time to cause the dis- 

 sociation of the organic molecules adjacent 



