928 



NATURE 



[DECeMBER 29, 1923 



and this will be reflected in the different degrees of 

 intersi-xuality resulting from different crosses. 



These facts, and various interesting consequences of 

 the facts, may be regarded as firmly established. It 

 should be noted that there arc one or two local races 

 which have given curious results, which will have to be 

 Worked out in greater detail. 



Goldschmidt's further argument is as lullovs.-,. The 

 expressions "2M>F" and "F>M" express only the 

 conditinii- in the fertilised eggs before development has 

 started, rhc further facts can be explained only 

 if we suppose that, during development, in each 

 cell of the body sex-controlling substances are pro- 

 duced at definite rates, and that these rates are pro- 

 portional to the original quantities of the sex-factors. 

 When, for example, a strong M and a weak F are 

 present together in an cu'l'. not only is the difference 

 F-M abnormally small. Ill It tin rite of increase of For 

 of substances produced by it is lower, that of M higher, 

 than usual. As a result, the two curves eventually 

 intersect ; and, of course, from this moment the 

 individual, hitherto female, is switched over to the 

 male type of development, and a female intersex is the 

 result. The degree of abnormality is of course deter- 

 mined h\- the relative rates of F- and M-production, 

 and tiir iKrisecjuent earlier or later incidence of the 

 intersection-point in the life-histor)^ 



If the intersection-point comes early enough, and the 

 change to the " wrong " sex occurs before any chitinisa- 

 tion has taken place, sex-reversal will be apparently 

 complete, and we shall get nothing but one sex from 

 our cross. This does occur. 



Let us suppose the sex-reversal is from female to 

 male. Then, in the resultant all-male broods, half the 

 individuals should be genetically females, and there- 

 fore be of chromosome-constitution XY instead of XX. 

 If mated with normal females,therefore,theyshould give 

 an abnormal sex-ratio (2XY= 9$ : iXX= c? : lYY 

 — dies), as was pointed out in general terms by Morgan 

 and by the reviewer some time ago. Similar sex- 

 reversal followed by abnormal sex-ratio in the next 

 generation has since been shown to occur by two 

 independent workers in the frog, and now Goldschmidt 

 has rung the changes upon it in Lymantria and has 

 shown that in ever>' case the results fit with expecta- 

 tion. Thus the final somatic sex may be the opposite 

 of the original zygotic sex. 



But we can go even further than that. The reversal 

 (total or partial) of the original sex may be due either 

 to genetic or to other factors. In Goldschmidt's 

 moths the reversal is due to genetic causes — the 

 fertilised egg contained ine\itably within itself the 

 seeds of its eventual change of sex, in the form of a 

 quantitative disharmony of the sex-determining factors. 

 NO. 2826, VOL. 112] 



But sex may be upset by outer agencies: by hormones, 

 in the case of vertebrates, whether the experiment be 

 of Nature's (as in the PVee-martin, the female intersex 

 of cattle, owing its abnormality to the male hormones of 

 its own twin brother), or of man's (as in the remarkable 

 castration and grafting experiments of Steinach, Sand, 

 Moore, Lipschiitz, Goodale, and others) ; by parasites, as 

 in crabs and insects ; or by interference with the gametes, 

 as in the increased numtxsr of males produced in frogs 

 (Hertwig and his pupils) or trout (.Mrsic) by over- 

 ripeness of the ova. 



The earliel- rigid belief that sex-determinati' 

 entirely a matter of the chromosome-constitutitm must 

 therefore be modified. Sex, in all higher animals and 

 in some plants, is normally determined by the chromo- 

 somes, but (as might have been foreseen) the normal 

 agency can in certain circumstances be overridden. 



It is clear that, with the point of view arising from 

 these facts, much that is lx)th new and important has 

 been gained. In the first place, we have the confirma- 

 tion of the idea, which had become establbhed as a 

 result of the work on Drosophila, especially by Bridges, 

 that sex-determination was an affair of balance between 

 genes contained in the sex-chromosomes and other genes. 



Bridges, by the utilisation of triploid strains, showed 

 that in the fly, while the female-determiner was mainly 

 lodged in the X (since here the female is XX, the male 

 XY), male-determination was not an affair of one but 

 of several factors, a disproportionate amount of in- 

 fluence being entrusted to that or those in the diminu- 

 tive 4th chromosome. Two X's in the presence of 

 three sets of autosomes gave intersexes: if only two 

 instead of three of the 4th chromosomes were pre- 

 sent, the intersexes were of more female type. We do 

 not profess to understand Goldschmidt's comments 

 (p. 99) : — " .... instead of speaking of the different 

 quantities of a sex factor he [Bridges] prefers to speak 

 of a more or less greater number of factors. Logically 

 as well as physiologically this is naturally the same." 



Although Goldschmidt has shown that his " F " 

 substance is largely due to factors lodged in the Y 

 chromosome, yet it may be confidently predicted that 

 numerous " sex-modifiers " will be discovered in the 

 autosomes. 



Our second principle is concerned with development. 

 Goldschmidt's idea of different rates of production of 

 substances in the embryo is in itself ver>^ fruitful, while 

 if his correlation of the rate of production of the sub- 

 stance with the amount of some initial ferment con- 

 tained in the gene, and this amount with the " potency " 

 of an allelomorph in a multiple series, — if this is sub- 

 stantiated, we acquire a new outlook into the relation 

 between Mendelian genes and their mode of action in 

 development. 



