No. 3.] PHENOMENA OF SEX-DIFFERENTIATION 485 



of Born^ and of Yung ^ on Amphibians, as to the influence of 

 nutrition in the determination of sexes, are well known to all 

 naturalists. 



The works of botanists in a similar line of observation are 

 highly instructive, but I cannot dwell on these topics at present. 

 The object of the present paper being only to bring out a cer- 

 tain illustration of general significance in connection with our 

 subject, an extensive multiplication of analogous instances is 

 not exactly to the point. 



From what has been said, it is clear that the differentiation 

 of sex in the developing embryo is purely an ontogenetic phe- 

 nomenon. Observing farther that the conditions of the sur- 

 roundings can effect such a determining influence as has been 

 described, we may say from one standpoint that the sex-differ- 

 entiation of the embryo is in the hands of external forces. On 

 the other side, the maleness or the femaleness of the organism 

 may be said to be the result of the responsive reaction on the 

 part of the given protoplasm to the external stimuli. The sex- 

 differentiation is, according to this view, due partly to a 

 property of the protoplasm as determined by its inherent struct- 

 ure, and partly to the action of definite external influences 

 which act upon the protoplasm from without. In this respect, 

 to anticipate my conclusion, I may say that tJie phenomenon of 

 sex-dijferentiation is one tvith that of irritability, and is tJie most 

 pronounced of all tJie phenomena of protoplasmic irritability, be- 

 catise the stimulus acts at an early stage of ontogeny, and tJius at 

 the outset profoundly deflects the course of behavior of the tvhole 

 organism. 



It seems rather superfluous to dwell, in this place, on the 

 well-established conception of the relation between the stimu- 

 lus and the protoplasmic reaction. If I touch briefly on this 

 subject, as I venture to do in the following, it is not with 

 the view of unnecessarily repeating what is already fully treated 

 in standard works on the subject, but to illustrate more fully 

 exactly what I mean by identifying the phenomenon of sex- 



^ G. Born, Experimentelle Untersuchungen iiber die E^itstchuttg der Geschlechts- 

 unterscheide, Breslauer arztliche Zeitschrift, 1 881. 



2 E. Yung, De Vinfluetice de la nature des aliments stir la scxualitc, Compt 

 Rend. Acad. Sci., Paris, T. xciii, 1881. 



