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 
