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 of 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 
eliminated from the egg or spermatozoén, 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 simplicity, 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 
tegards the germ-cell as either purely male or female; but here 
