THE GERM-PLASM TPIEORY 401 



cell in which they become active, causing it to vary in such a manner 

 that the formation of the relevant part results. While I conceive of 

 development as a continuous process, I supplement this with the idea 

 that from within, namely, from the nuclear substance, new, directive, 

 ' determining ' influences are continually being exerted on the de- 

 veloping cells. 



I can hardly think of a better proof of the necessity of this 

 assumption than that furnished by Delage, one of the most acute 

 biologists of France, who, in his comprehensive book on Heredity, has 

 striven to replace the theory of determinants by something simpler. 

 Delage rejects all 'primary constituents' (Anlagen) in the germ, all 

 ' particules representatives,' as much too complicated an assumption, 

 and thinks it possible to work with the conception of a germ-plasm 

 which is about as simple as the cell-substance of a Rhizopod, that is 

 to say, a protoplasm of definite chemico-physical constitution and 

 composition. Leaving out of account the consideration that the 

 protoplasm of an amoeba is scarcely of such extreme simplicity, but 

 is certainly made up of numerous differentiated and definitely 

 arranged biophors, how could such an extremely simple (' dminemment 

 simple ') constitution of the ovum as is here assumed give rise to such 

 a complicated organism, the individual parts of which are capable of 

 independent and transmissible variation? According to Delage it 

 does so because the ovum, though not containing ' all the factors 

 requisite for its ultimate resultant,' does contain ' un certain nombre 

 des facteurs ndcessaires k la determination de chaque partie et de 

 chaque caract^re de I'organisme futur ' ! Determinants after all, it 

 may be said, but that is far from the truth ! It is not primary con^ 

 stituents that the germ contains, according to Delage, it is chemical 

 substances, for instance muscle substances, probably 'les substances 

 caractdristiques des principales categories de cellules, c'est-a-dire, 

 celles qui, dans ces cellules, sont la condition principale de leur fonc- 

 tionnement.' All these must be contained in the ovum. How they 

 are to reach their proper place in the organism, how the 'charac- 

 teristic chemical substance ' of a mole is to land just behind the right 

 or left ear of the fully formed man, is not stated. But apart from 

 this, there is a much deeper error in this assumption of specific 

 chemical substances in the ovum as an explanation of the phenomena 

 of local hereditary variation, and I have already touched upon it: 

 chemical substances are not vital units, which feed and reproduce, 

 which assimilate and which bear a charm against the assimilating 

 power of the surrounding protoplasm. They would necessarily be 

 modified and displaced in the course of ontogeny, and would therefore 



