Heredity. 151 



" The true and ultimate causa efficiens of the biogenetic 

 process, I propose to designate by a single word, Peri- 

 genesis the periodic wave-generation of the organic 

 molecules or plastidules." The tendency that this 

 periodic motion has to persist, preserving as it were a 

 characteristic rhythm, explains the relative constancy 

 of ordinary inheritance, while at the same time the 

 results of new experience may be added on to the domi- 

 nant molecular movement. In very simple organisms, 

 as he says, the plastidules have, so to speak, learned 

 little and forgotten nothing, while in highly-perfected 

 types the plastidules have both learned and forgotten 

 much. 



According to Jaeger the continuity is protoplasmic, 

 and is effected after the ordinary fashion of cell-division. 

 To this there has to be added his chemical conception 

 of pangenesis, which, when expressed in more modern 

 phraseology, is the supposition that characteristic 

 chemical substances find their way to the reproductive 

 elements, and make these, to some limited extent, 

 sharers in the general life of the organism. 



Galton does not make the continuity much more pre- 

 cise than is implied in the general statement that a 

 residue of the germs, gemmules, or organic units in the 

 "stirp", remaining latent in the construction of the 

 body, are passed on into the reproductive elements, and 

 keep up a continuity between "stirp" and "stirp". 

 In regard to the future history of the gemmules, Galton 

 supposes that they form groups in the ovum, and be- 

 come directly associated with its division, while at later 

 stages they wander and give rise to new cells. To 

 obviate histological difficulties, Herdman proposes the 

 following reasonable amendment, "that the body of the 

 new individual is formed, not by the development of 

 gemmules alone and independently into cells, but by the 

 gemmules in the cells causing, by their affinities and 

 repulsions, these cells so to divide and redivide as to 

 give rise to new cells, tissues, and organs ". Brooks 

 and Nussbaum rest satisfied in maintaining a cellular 

 continuity. 



What keeps up the continuity, according to Weis- 



