420 Experimental Zoology 



Conclusions 



We have examined the principal data that bear on the problem 

 of sex determination and have found that we still lack the clew 

 that solves the riddle. Nevertheless many important facts that 

 bear directly on this question have been made known, and the 

 ground has been pretty well broken for future investigation. 

 Concerning the various hypotheses that have been proposed, we 

 may place them under two principal headings, which I shall call 

 the morphological and the physiological points of view. Let us 

 examine these in turn. 



The Morphological Conception oj Sex Determination 



According to this view, the characters that stand for the male 

 or the female condition are represented in the germ-cells as pre- 

 existing elements. If we assume that the male characters are 

 ehminated from the egg or spermatozoon, the female characters 

 remaining, the egg produces a female ; if the female elements are 

 ejected, the egg becomes a male. This method of treating the 

 problem has the advantage of simpHcity, and is capable of dia- 

 grammatic treatment. It is the method that has been largely 

 followed by modern theorists. The same principle has been 

 followed in recent years in dealing with the entire problem of 

 heredity. The most serious objections to this procedure are 

 that it is based on an assumption that cannot be verified, and in 

 practice it has not solved, except in a purely formal way, any 

 of the problems of heredity. The problem instead of being 

 solved is merely shifted into an unknown field where the imagi- 

 nation has full sway and where the conclusions cannot be 

 tested. 



A modified form of this same method of treatment is to regard 

 heredity as the result of the dominance of one or of the other sex- 

 characters, both unit-characters being assumed to be present in 

 the same egg and sperm. There are certain facts that seem to 

 indicate that this is an advance over the other point of view that 

 regards the germ-cell as either purely male or female ; but here 



