150 The Science of Life. 



complex in structure, but has nevertheless great powers of per- 

 sistence and of growth. 



It may now be concluded that in the more or less 

 strict continuity of the successive sets of reproductive 

 Elaborations e l ements li es the solution of the main problem 

 of the idea of of heredity. This appears the most con- 

 alty ' venient place to notice various suggestions 

 made as to what it is exactly that is continuous. The 

 earlier of these suggestions were brought forward indeed 

 before the notion of continuity had its present definite 

 form, but it seems appropriate to introduce them here. 



The Memory Theories. Prof. Hering in Prag and 

 Mr. Samuel Butler in England suggested about the 

 same time a psychical aspect of the hereditary continu- 

 ity. The two suggestions may be so far summed up 

 together. Memory is a general function of organized 

 matter, and the reproduction of parental likeness is the 

 result of unconscious recollection of the past. What 

 are ordinarily called memory, habit, instinct, and em- 

 bryonic reconstruction are all referable to the memory 

 of living matter. Hering finds the basis of this uncon- 

 scious memory in the persistence of the undulatory 

 movements supposed to be characteristic of the mole- 

 cules. These undulations are sensitive to change, and 

 room is thus left for variability, but their tendency to 

 persist in their established harmony is the basis of 

 heredity. 



Ha3ckel also emphasized the luminous metaphor of 

 "organic memory", and sought to express it in terms 

 of molecular motion. His theory is summed up in the 

 characteristic phrase " perigenesis of the plastidules ". 

 Comparing the course of phylogenetic development to a 

 complex, ramified series of wave-lines, in which a single 

 life is represented by a single wave, he imagines a simi- 

 lar ontogenetic wave-motion in the development of the 

 individual. "The developing impulse which in the one 

 case is transferred from the ancestral species to the 

 whole group of species, and in the other case from the 

 ancestral cell to the entire group of cells, assumes in 

 both cases the same form of a branching wave-motion. " 



