226 THE PRINCIPLES OF HEREDITY 



arisen in connection with a highly-developed nervous system, 

 which owed its existence to the evolution of many reflexes 

 within the same complex organism. Sensation, as we have 

 already surmised, must probably have preceded instinct as an 

 accompaniment of elaborate reflex action. When during the 

 course of subsequent evolution sensation took on particular 

 tones or qualities those of pleasure and pain, the inciters of 

 desire instinct made its appearance. It is equally difficult 

 to indicate the earliest appearance of reason of memory and 

 its corollary, the power of applying the contents of memory 

 to the guidance of future conduct. A rudimentary power of 

 making mental acquirements seems to exist even so low in 

 the scale as the lower mollusca. " Even the headless oyster 

 seems to profit from experience, for Dicquemase (Journal de 

 Physique, vol. xxviii., p. 244) asserts that oysters taken 

 from a depth never uncovered by the sea, open their shells, 

 loose the water within, and perish ; but oysters taken from 

 the same place and depth, if kept in the reservoirs, where they 

 are occasionally left uncovered for a short time, and are 

 otherwise incommoded, learn to keep their shells shut, and 

 then live for a much longer time when taken out of the 

 water." x 



384. Accordingly as animals are more and more highly 

 placed in the scale of life their power of making mental 

 acquirements, and therefore of profiting by experience, in- 

 creases. Without exception it is small in the case of all animals 

 that are not tended during at least a part of their conscious 

 life by the parents. Such animals, cast adrift, must neces- 

 sarily arrive in a hostile world with their faculties fully 

 developed. From the beginning they must be capable of 

 fighting their own battles. They have little time to learn, 

 and therefore little capacity for learning. If they had, since 

 they generally die after depositing their eggs, they would 

 have no opportunity of imparting anything they had learnt 

 to the next generation. They must come, therefore, armed 

 cap-a-pie with instinct for the fray. Some of these animals, 

 however, display distinct though very limited capabilities 

 for making mental acquirements. Thus trout in a much- 

 fished stream grow shy of moving objects on the bank, and 

 carp confined in monastic ponds are said to have learned to 

 recognize the sound of a bell as a signal for food. Amphibians 

 and reptiles have been tamed and have even learned to 

 distinguish their masters from other people. 



385. In the case of animals that tend their young the 



1 Romanes, Animal Intelligence, p. 25. 



