No. 3-] PHENOMENA OF SEX-DIFFERENTIATION. 489 



ents is not entirely consumed for the building up of the individ- 

 ual animal. A small portion of it goes to the formation of the 

 germ-cell, which later develops into the sperm-cell or the egg- 

 cell, as the case may be. Thus the parts of an individual organ- 

 ism become divided into two fundamentally different structures 

 which have been called by Weismann the ^^ soma'' and the 

 "germ." Galton ^ designated these two parts of the organism 

 as the "/«/^«^ " and the '^latent'' part respectively; Jager,^ as 

 the '' ontogenetic part'' and the '' phylogenetic part" ; and Rauber,^ 

 as the '^ personal part" and the '^ germinal part." 



There are several other eminent naturalists who have given 

 expression to a similar view on this subject, but it is entirely 

 unnecessary to enter into any historical review of the ques- 

 tion at present. The point which is most important to us is 

 the bearing of such a view of animal organization upon the 

 question we have been considering. If the phenomena of 

 sex-differentiation of the organism were to be identified with 

 that of the irritability of an organ which regains its original 

 irritable state after a short interval of restitution, it is evident 

 that the period covered by the life-history of the individual 

 organism of both sexes must be considered as one long con- 

 tinuous series of the reactions of the protoplasm to the sur- 

 roundings. The return of the whole organism to its original 

 irritable stage, as has already been stated, is accomplished by 

 the formation of the unicellular embryo or by the union of two 

 sexual cells which were reserved in the " germinal part " of the 

 male and female organism. The period, then, covered by the 

 manifestation of irritable phenomena in a matured organ is com- 

 parable to the whole life-history of the growing organism ; and 

 the recurrence of the irritable condition in the organ corresponds 

 to the production of the unicellular embryo, which is ready to 

 repeat in turn a series of developmental phenomena similar to 

 those which its parents had already undergone before it. There 

 is really no fundamental difference between the irritability of 

 the growing organism and that of the organ. 



1 Galton, On Blood Relationship, Proc. Roy. Soc, XX, 1872. 



2 Jager, Physiologische Briefe iiber Vererbung, reprinted in his Lehrbuch der 

 allgem. Zoologie, II, 1878. 



3 Rauber, Personaltheil unci Germinaltheil des Individuums, Zool. Anz. IX. In 

 this paper Rauber gives references to his earlier writings on the subject. 



