SELECTION 137 



natural selection. 32 Nevertheless, we have seen that 

 habits are often transmitted ; and, if changes in 

 brain structure can be handed down from parent to 

 offspring, we cannot doubt but that other bodily 

 structures are handed down also. But all habits are 

 due to psychogenesis, and it seems probable that 

 only those structures can be handed down which 

 have been originated by a mental impulse. This 

 would be quite in accordance with Bering's theory. 

 The means by which it is done have also been ex- 

 plained by Professor Hering, as I have already 

 stated. It is not a direct action, and it requires con- 

 stant repetition to make an impression ; but in time 

 resistance is overcome and a permanent structure 

 is developed. This is what Darwin was looking for 

 when discussing the indirect effect of external 

 agencies. 



I have found it very hard indeed to discover any 

 undeniable evidence of the transmission of acquired 

 characters ; for even among useless characters it is 

 difficult to find any which are undoubtedly due to 

 the action of physiogenesis. Perhaps the bright 

 colours of alpine flowers is a good example, for they 

 are thought to have been produced by special 

 climatic conditions, and they are regularly trans- 

 mitted in plants which have been removed to the 

 plains. The brightly coloured birds and insects of 

 tropical regions may also be admitted. For 

 although there are many dull coloured species among 

 them, these belong mostly to the primitive families, 



32 See Weismann on "Heredity," vol. i., Essay vii., 

 p. 397. 



