62 Animal Life and Intelligence. 



difficult for the human mind to grasp all the interlacing 

 threads of causation at a single glance, men of science 

 have endeavoured to isolate their several strands, and, 

 applying the principle of analysis, without which reasoning 

 is impossible, to separate out the factors and determine 

 their laws. In this chapter we have to consider some of 

 the factors of organic progress, and endeavour to determine 

 their laws. 



The law of heredity may be regarded as that of persistence 

 exemplified in a series of organic generations. When, as 

 in the amoeba and some other protozoa, reproduction is by 

 simple fission, two quite similar organisms being thus pro- 

 duced, there would seem to be no reason why (modifications 

 by surrounding circumstances being disregarded) hereditary 

 persistence should not continue indefinitely. Where, how- 

 ever, reproduction is effected by the detachment of a single 

 cell from a many-celled organism, hereditary persistence * 

 will be complete only on the condition that this reproductive 

 cell is in some way in direct continuity with the cells of 

 the parent organism or the cell from which that parent 

 organism itself developed. And where, in the higher 

 animals, two cells from two somewhat different parents 

 coalesce to give origin to a new individual, the phenomena 

 of hereditary persistence are still further complicated by 

 the blending of characters handed on in the ovum and the 

 sperm ; still further complication being, perhaps, produced 

 by the emergence in the offspring of characters latent in 

 the parent, but derived from an earlier ancestor. And if 

 characters acquired by the parents in the course of their 

 individual life be handed on to the offspring, yet further 

 complication will be thus introduced. 



It is no matter for surprise, therefore, that, notwith- 



* Samuel Butler iu England, and Ewald Hering in Prague, have in- 

 geniously likened this hereditary persistence to " organic memory." What 

 are ordinarily called memory, habit, instinct, and embryonic reconstruction, 

 are all referable to the memory of organic matter. The analogy, if used with 

 due caution, is a helpful one, what we call memory being the psychical aspect 

 (under certain special organic and neural conditions) of what under the 

 physical aspect we call persistence. 



