i RESULT OF THE DISCUSSION 91 



and then there is the possibility, as we shall explain 

 further on, that the part played by chance is much 

 greater in the variation of plants than in that of 

 animals, because, in the vegetable world, function 

 does not depend so strictly on form. Be that as it 

 may, the neo-Darwinians are inclined to admit that the 

 periods of mutation are determinate. The direction 

 of the mutation may therefore be so as well, at least in 

 animals, and to the extent we shall have to indicate. 



We thus arrive at a hypothesis like Eimer s, 

 according to which the variations of different characters 

 continue from generation to generation in definite 

 directions. This hypothesis seems plausible to us, 

 within the limits in which Eimer himself retains it. 

 Of course, the evolution of the organic world cannot 

 be predetermined as a whole. We claim, on the 

 contrary, that the spontaneity of life is manifested by 

 a continual creation of new forms succeeding others. 

 But this indetermination cannot be complete ; it must 

 leave a certain part to determination. An organ like 

 the eye, for example, must have been formed by 

 just a continual changing in a definite direction. 

 Indeed, we do not see how otherwise to explain the 

 likeness of structure of the eye in species that have 

 not the same history. Where we differ from Eimer 

 is in his claim that combinations of physical and 

 chemical causes are enough to secure the result. We 

 have tried to prove, on the contrary, by the example of 

 the eye, that if there is &quot; orthogenesis &quot; here, a psycho 

 logical cause intervenes. 



Certain neo-Lamarckians do indeed resort to a 

 cause of a psychological nature. There, to our think- 



(Anne&quot;e psychologique, vol. xii., 1906, pp. 95 ff.), and De Vries, Species and 

 Varieties, p. 655. 



