Jahuaet 8, 1909] 



SCIENCE 



69 



bolie processes. It is, therefore, well within 

 the range of possibility that the reaction 

 between egg and spermatozoon may differ 

 in respect to the two classes. Such physi-. 

 ologieal differences may vary in different 

 species and may be capable of modification 

 by external agents acting upon either sex. 

 Again, the difference of mortality between 

 the sexes, which is probably one of the 

 modifying factors of the sex-ratio, may 

 perhaps be traceable to differences of 

 metabolism that have their original root in 

 the sexual difference of nuclear constitu- 

 tion. In the directions here indicated lie 

 many possibilities regarding the natural or 

 artificial modifications of the typical sex- 

 ratio of which no account has hitherto been 

 taken. Until they have been thoroughly 

 reckoned with, I think that all results upon 

 the sex-ratios that are based upon general 

 statistical and experimental inquiries must 

 be taken with great caution. Taken as a 

 whole, the evidence now indicates that in 

 diecious organisms generally the basis of 

 sex-production is primarily adapted for the 

 production of males and females in equal 

 numbers, and that departures from equal- 

 ity are due to secondary modifications. 



Vin. CONCLUSION 



A review of the ground that has been 

 traversed will, I think, leave no doubt re- 

 garding the answer that should be given to 

 the general question that formed our point 

 of departure. The conclusion has become 

 in a high degree probable that sex is con- 

 trolled by factors internal to the germ- 

 cells, that the male or female condition 

 does not arise primarily as a response of 

 the developing germ to corresponding ex- 

 ternal conditions. Such conditions may 

 operate to modify the action of the internal 

 mechanism, but the process of sex-produc- 

 tion is fundamentally automatic. In so far 

 as sex has been traced to a predetermina- 



tion of the fertilized egg, or to a predestina- 

 tion of the gametes that unite to produce it, 

 the problem of sex-production may be said 

 to have reached a proximate solution. But 

 it is perfectly obvious that this solution is 

 proximate only, and has but opened the 

 way to a more searching analysis of the 

 nature of sex. Upon what conditions with- 

 in the fertilized egg does the sexual differ- 

 entiation depend? In some way, we may 

 now be reasonably sure, upon the physio- 

 logical reactions of nucleus and protoplasm ; 

 but the same may be said of any other form 

 of heredity. The specific problem of sex 

 here merges into the larger one of heredity 

 and differentiation in general, and the 

 minor problem acquires a broader interest 

 through the hope that it gives us of attain- 

 ing a solution of the major one. Into this 

 aspect of the subject I will not now enter. 

 I hope to have given some justification for 

 the assertion, made at the outset, that sub- 

 stantial progress has been made in the exact 

 analysis of the sex-problem. Eecent re- 

 searches have given good reason to believe 

 that sex-production is governed by a com- 

 mon, and perhaps relatively simple prin- 

 ciple. They have demonstrated that it has 

 a definite morphological basis, which, even 

 though its mode of action is not yet fully 

 comprehended, is susceptible of accurate 

 microscopical and experimental analysis. 

 They have given a new point of view for 

 the experimental and statistical analysis of 

 the problem. And the progress already 

 made encourages us to hope that a more 

 complete solution may not be very far 

 away. 



The history of the subject throws an in- 

 teresting light upon the methods of biolog- 

 ical inquiry. The reform that is taking 

 place in zoology through the extension of 

 the experimental method has sometimes 

 produced a disposition to exalt this method 

 above others, and the same may be said in 



