496 THE AMERICAN NATURALIST [Vol. XLIV 



ther test. This is the position we are in to-day concern- 

 ing the interpretation of the mechanism that we have 

 found by means of which sex is determined. I could, by 

 ignoring the difficulties and by emphasizing the impor- 

 tant discoveries that have been made, have implied that 

 the problem of sex determination has been solved. I 

 have tried rather to weigh the evidence, as it stands, in 

 the spirit of the judge rather than in that of the advo- 

 cate. One point at least I hope to have made evident, 

 that we have discovered in the microscopic study of the. 

 germ cells a mechanism that is connected in some way 

 with sex determination; and I have tried to show, also, 

 that this mechanism accords precisely with that the ex- 

 perimental results seem to call for. The old view that 

 sex is determined by external conditions is entirely dis- 

 proven, and we have discovered an internal mechanism 

 by means of which the equality of the sexes where equal- 

 ity exists is attained. We see how the results are auto- 

 matically readied even if we can not entirely understand 

 the details of the process. These discoveries mark a dis- 

 tinct advance in our study of this difficult problem. 



