Internal Factors of Sex Determination 421 



also we lack the clew that tells us in what condition the charac- 

 ters are represented in the egg. 



The Physiological Conception of Sex Determination 



From this point of view we may consider the protoplasm as 

 a substance capable of assuming one or another condition that 

 is determined, for the time being, by the environment or by inter- 

 nal conditions. We may suppose that the same end-result 

 (sex, for example) may be determined by different factors in 

 different species. I mean that while in certain species one kind 

 of factor commonly determines the result, in other species other 

 factors may determine which of the possible alternatives is fol- 

 lowed. The protoplasm may be looked upon as being in a con- 

 dition of equilibrium as far as the adoption of either alternative 

 is concerned, and which one is followed is determined by those 

 conditions that bring to the front the one or the other possible 

 state. 



An illustration may make this clearer. In certain male crabs 

 the right and left chelae are different in structure. In some 

 species it is always the right-hand claw that is the larger, in 

 others the left, while in some cases either the right or the left is 

 the larger. It has been shown by Przibram for some species of 

 the latter class that if the large chela is removed the small one 

 becomes the larger at the next molt, and in place of the large one 

 removed a small one regenerates in its place. Both claws have 

 potentially the same possibilities of becoming large or small. 

 External or internal conditions determine which kind of develop- 

 ment takes place ; but the selection once made, the differentiation 

 proceeds strictly along one line. 



Now in this case we might assume that when the big claw of one 

 side is removed, all the preformed elements (primoidia) of the 

 big claw contained in all the cells of the small claw begin to 

 develop and dominate and replace the already-controlling-small- 

 claw-forming elements. That is the morphological way of ex- 

 plaining the result. On the other hand, the other the physio- 

 logical idea makes use of no such mechanism, but assumes 



