464 Genetics of Sex Determination 



Crosses of females with such secondary males give no different result 

 from ordinary matings. But in one case males could be transformed 

 into females by amputation of the sex segments and regeneration. 

 Females can easily be changed into males by amputation of the pos- 

 terior end or the head. In younger stages they even change sex as a 

 consequence of hunger or high temperature. Isolation of females 

 (prevention of copulation) also makes them change into males. This, 

 then, is considered a typical example of phenotypic sex determination. 

 In discussing the facts the author states first that the finding that 

 the monoecist never forms egg and sperm cells simultaneously re- 

 quires a special genetic condition, in addition to the F/M balance 

 which controls sex. However, he thinlcs that in other worms or mol- 

 lusks, where both sexual products are formed simultaneously or con- 

 secutively, real phenogenetic sex determination occurs. In Bonellia or 

 Gnibea, where only one sex functions in one individual, we are near 

 to the situation in Amphibia with a little F/M imbalance and second- 

 ary modifiability, that is, a transition between genotypic and pheno- 

 typic sex determination. It seems to me obvious that in all the exam- 

 ples here discussed (Bonellia, with two alternative sexes decided by 

 the presence or absence of a chemical action upon young larvae; 

 Sagitta, with both sex cells present simultaneously; Ophryotroclia 

 and mollusks, with a more or less complicated consecutive change 

 from suppression of one sex to that of the other by external conditions, 

 age, or an inherited order; Grubea, with the mentioned limitations of 

 sex change) specific genetic determiners control the special t^'pe of 

 internal environment in space and time which sets the norm of reac- 

 tion of the F and M determiners. To call this phenotypic sex deter- 

 mination is rather absurd and can only lead to confusion. Hauenschild, 

 after breaking a lance for phenotypic sex determination, tells us fur- 

 ther on that the different reactions of females and males in individual 

 cases are based upon a whole complex of factors which enhance 

 female or male determination and the equilibrium of which can be 

 shifted by external conditions. Finally it is admitted that it could also 

 be possible that not all individuals are real monoecists but are genet- 

 ically weak males. Or the possibility exists that certain genie com- 

 binations shift (by some physiological process) the equilibrium of 

 non-hereditary factors. Again we see the lack of usefulness of the 

 idea of phenotypic sex determination when nothing is visible (and 

 discussed) but a monoecic, hermaphroditic genetic constitution with 

 all kinds of genetic and non-genetic influences upon the internal en- 

 vironment which is the partner of genie action in a norm of reaction; 



