ORGANIC EVOLUTION — MENTAL 153 



It is extremely doubtful whether the lowest verte- 

 brates have any power of acquiring mental traits, of 

 varying mentally so as to place themselves in greater 

 harmony with the environment. But, a little higher in 

 the scale, reason certainly appears, and gradually over- 

 shadows reflex action and instinct, its growth being 

 synchronous and related to that of the higher portions 

 of the brain, the cerebrum and the cerebellum, especi- 

 ally the former. The lower vertebrates, like the lower 

 insects, and unlike the higher vertebrates and insects 

 (e. g.) ants and bees, do not generally tend their young, 

 and therefore can teach them nothing. By virtue of a 

 knowledge which is inborn and hereditary, and which 

 cannot possibly have been acquired, they deposit their 

 eggs imder circumstances favourable for survival {e. g. 

 most fish), and by virtue of a similar knowledge, the 

 young when they emerge from the egg are fully 

 equipped mentally for the battle of life. Some fish 

 (e. g. sticklebacks), however, protect their young for a 

 few days after they are hatched, during which time the 

 latter may acquire from their parents such traits as 

 watchfulness against enemies, knowledge of shelter, &c. 

 That little is acquirable by fish is known to every 

 keeper of an aquarium, but that they have some small 

 power of mentally varying, so as to place themselves in 

 harmony with an environment which has become more 

 complex, is proved by such facts as that they may be 

 tamed to a limited extent, and that the wariness of 

 trout increases in a much-fished stream. 



Batrachians show distinct powers of acquiring mental 

 traits. Many frogs and toads have been tamed. The 

 following is an extreme case. 



" I used to open the gate in the railings round the 

 pond, and call out ' Tommy ' (the name I had given 

 it), and the frog would jump out from the bushes, dive 



