258 SECRETS OF ANIMAL LIFE 



at some length with the resemblance between the 

 scallop's eye and the vertebrate's eye, pointing out 

 the difficulties in interpreting this in terms of the 

 selection of accidental variations either insensible 

 or considerable in amount, or in terms of an inter- 

 action of internal and external forces, or in terms of 

 use-inheritance. Without denying that each of these 

 theories may be " true in its way," he argued that 

 it was necessary to supplement them by the idea 

 of a common " original impetus/' which is the 

 fundamental cause of heritable variations. But Pro- 

 fessor Bergson unfortunately exaggerated the re- 

 semblance between the eye of the backboned animal 

 and the "eye" of the scallop; except the "in- 

 version of the retina " they have little in common. 

 Moreover, the scallop's numerous eyes may not 

 be eyes at all, in the strict sense. We do not think 

 that Professor Bergson did justice to the subtlety 

 of even the orthodox Darwinian position, or to 

 the facts which have saved the neo-Darwinian, at 

 least, from being shut up to a belief in " accidental " 

 variations, or the role that the organism plays 

 as a genuine agent in testing its germinal variations 

 in reference to environing conditions which it has 

 a share in selecting. But we think he was right in 

 thinking that the interpretation of convergence is 

 not altogether plain sailing. 



If one plays long enough with cards one will 

 repeat identical hands, and if a certain type of 

 structure is the only one adapted to certain circum- 

 stances, or is far and away fitter than any other 



