38 Heredity. 



Erblichkcit ist das Gedachtniss der Plastidule, die Ya- 

 riabilitat is die Fassungskraft der Plastidule). The one 

 brings about the constaucy and the other the diversity 

 of organic forms. In the very simple and persistent 

 forms of life the plastidules have, so to speak, learned 

 nothing and forgotten nothing. In highly perfected 

 and variable organisms the plastidules have both learned 

 and forgotten much.'' 



This somewhat long quotation contains a thorough 

 and exhaustive statement of the perigenesis hypothesis, 

 and it is therefore interesting to notice that its only real 

 claim to recognition as a true explanation of the phe- 

 nomena of heredity is based upon or at least demands 

 the acceptance of some form of the evolution hypoth- 

 esis. 



EowcTer great may be the importance of the analogy 

 between the gradual evolution of the sjiecies by the 

 specialization of the constituent individuals, and the de- 

 velopment of the individual by the specialization of cells, 

 and plastidules, we have already pointed out that it is 

 in no sense an explanation of the latter, since the real 

 cause of the evolution of the species, the selection of 

 cono^enital variations, is absent. • 



The only part of Haeckel's hypothesis of perigenesis 

 which has any claim to be considered an explanation of 

 the reproductive power of animals, is the statement that 

 heredity is memory, and variability the acquisition of 

 new experiences. Stated hy itself, without explanation, 

 this may seem to those w-ho are unfamiliar with the sub- 

 ject very much like nonsense, for the profound truth 

 npon which it rests is not at all obvious at first sight. 



Herbert Spencer has, in his masterly discussion of the 

 nature and distinctive characteristic of life, given us, 

 as the sum and substance of his analvsis, the statement 



