350 



The Journal of Heredity 



about metamorphosis. Uhlenhuth be- 

 Heves that a definite "excretor sub- 

 stance" is produced in some organ of 

 the body as the resuh of general 

 somatic differentiation, and that this 

 affects the thyroid and causes it to 

 Hberate its secretion. 



This, I must confess, appears to me 

 to give no more than a formal ex- 

 planation of the phenomena, and, 

 furthermore, to be unnecessarily com- 

 plicating matters. I may be pardoned 

 if I digress for a few moments to an- 

 other field for illustrations which I 

 believe will throw light on the prob- 

 lem. 



As is well known, Goldschmidt* has 

 made a careful study' of the sexually 

 abnormal individuals produced by cer- 

 tain crosses between the European and 

 Japanese races of Lymantria, the 

 Gipsy Moth. He showed by a careful 

 analysis that they could only be ex- 

 plained as individuals which have be- 

 gun their lives as members of one 

 sex, but had, at some time in their 

 development, come to a critical point 

 after which they continued to develop 

 as members of the other sex. The 

 commonest types of abnormal indi- 

 viduals are those which start as fe- 

 males, but finish as males. Since the 

 chitinous hard parts of an insect are 

 permanent, those which are laid down 

 during the "female" part of the de- 

 velopment persist even after "male" 

 development has begun. Soft parts, 

 however, such as the gonads, undergo 

 a reconstructive process. If the crit- 

 ical point occurs early, before the 

 formation of any chitin, complete sex- 

 reversal takes place, and all individ- 

 uals produced are of one sex. 



Analysis shows clearly that this 

 type of sexual abnormality, whether 

 it leads to complete sex-reversal, or 

 to the intermediate condition of inter- 

 sexuality, is due to the association of 

 genetic sex factors of ditterent 

 "strength" or "potency." It is further 

 clear that in moths, the male-determining 

 factor is lodged in the sex-chromo- 

 some, so that the males possess two 

 such factors, the females, one. The 



location of the female-determining 

 factor is less certain. It appears to 



be inherited purely maternaiiy. ( io'd- 

 schmidt believes it to be contained 

 in the Y-chromosome, which in moths, 

 where females are heterogametic, is 

 confined to females ; and to act on 

 the cytoplasm of the egg before fer- 

 tilization. Be that as it may, it ap- 

 pears to be definitely proved that it 

 is inherited in the female line only, 

 and that the amount of this factor 

 present is the same in males and te- 

 males. 



In males there is thus a double dose 

 of male-detennining factor — call it 

 M — to a single dose of female-deter- 

 mjning factor, F ; further, 2 M is more 

 effective than F. Translated into or- 

 dinary terms, this would imply that 

 the factors M and F are normally re- 

 sponsible for the continuous produc- 

 tion of two substances, say U and 0, 

 which are responsible for the devel- 

 opment of maleness and femaleness 

 respectively, and that the total of U 

 produced by 2 ikf is so much in excess 

 of the amount of O produced by F 

 that normal males are the result. Con- 

 versely in normal females, there is a 

 single dose both of M and F ; and 

 further F is greater in its effect than 

 M; and so O is produced in excess, 

 and can exert its effects and give rise 

 to females. 



The commonest type of intersex, 

 that which starts as female and ends 

 as male, is an individual in which a 

 slow-working F is combined with a 

 fast-working M factor. This implies 

 that the curve of 0-production is de- 

 pressed, that of 17-production raised ; 

 this in its turn will mean an intersec- 

 tion of these curves during or before 

 the formative period when differentia- 

 tion is occurring, so that an original 

 excess of is succeeded by a later 

 excess of U and the animal changes 

 from female to male. The converse 

 change from original male to the later 

 female development scarcely ever oc- 

 curs unless tivo slow-working M's are 

 associated with a fast-working F, and 



