THE THEORY OF LAMARCK 39 



in the position of the eye could be of no advantage 

 so long as this organ remained upon the under surface. 

 The very young fish, whilst still symmetrical, are 

 known sometimes to fall upon one side, and when in 

 this position to twist the lower eye forcibly upwards. 

 Darwin himself therefore supposed that the origin of 

 the adult structure is to be attributed to the inherited 

 effect of efforts of this kind. 



The interest of the last case lies in the fact that it 

 relates to a structure, the origin of which does not 

 appear explicable on the theory of natural selection ; 

 its bearing will therefore be better understood when 

 we come to discuss that theory in the next chapter. 



The inherited effects of voluntary striving can clearly 

 have no application to the case of plants. Lamarck 

 therefore supposed that evolution in the vegetable 

 kingdom had taken place entirely through the action of 

 external agencies upon plants. The soil, for example^ 

 in which a plant grows has a direct influence upon its 

 form. Altitude, moisture, heat, and light are other 

 important factory and the effect of their influence upon 

 the plant was supposed by Lamarck to be inherited. 

 The shape of irregular flowers was regarded as having 

 been directly caused by the strains and pressures 

 occasioned by bees and other insects whilst making 

 their visits in search of honey or pollen. 



Lamarck's theory turns entirely upon the question 

 whether acquired characters are inherited, and if so, 

 to what extent, siiwe, if such inheritance is shown to 

 be extremely slight, the cause t though a true one, 

 may be insufficient to explain the effects attributed 



