even as perfect as the eye of an eagle might be formed by natural 
selection — his reason ought to conquer his imagination.” In this 
argument, or rather statement, Darwin takes his variations for 
granted, and it is in the production of these variations that both 
Drieseh and Bergson believe their special factors manifest them- 
selves. The whole thing is in reality only another form of the pro- 
blem that we discussed first, i.e., the development of form after the 
fertilisation of the ovum. The conclusions to be drawn from the 
discussions on the evolution of such a complicated organ as the eye 
are in a way disappointing. We can find no exceptional support, 
however, for Bergson or Drieseh in the comparison, made 
so keenly by Bergson, of the eye of Pecten with the 
human eye. So far as the evolution of either of these eyes 
is concerned many biologists will follow Darwin and take 
chance variations as sufficient, if natural selection eliminates 
the useless, to account for the final evolution of such complex struc- 
tures. Others would probably assert that nothing but large varia- 
tions or mutations had been at work without attempting to inquire 
further into the co-ordination present in such mutations. The pro- 
blem in either case is one of variation, and we have no evidence yet 
explaining the phenomena of variation. We are most certainly not 
in a position to say that some non-material factor such as Driesch’s 
“Entelechy” or Bergson’s “Vital Impetus” is present or even neces- 
sary, although no satisfactory mechanical explanation of variation is 
forthcoming. 
Before leaving the subject which has introduced the eye of the 
mollusc Pecten into this discourse let me call your attention to one 
or two other points of interest in connection with the evolution of 
these structures. As a lamellibranch sense-organ the complexity of 
the eye of the scallop requires some explanation. T am afraid the 
theory of evolution by natural selection often encourages us to look 
with an anthropocentric attitude at the phenomena of adaptation. 
If so, we can find no solace in this case. There is no evidence of 
the need of such a battery of highly complicated visual organs. 
Other bivalves with similar habits are not provided with them. 
Lima swims as well as Pecten and has extremely simple eyes. Spon- 
dylus has eyes like Pecten and does not swim at all. Experiment, 
too (although personally I think in this particular example it is 
almost; worthless unless the conditions are more natural than is usu- 
ally the case) fails to show any reason for the presence of such eyes. 
How then are they to be explained on the assumption of a survival 
of the fittest, or on being the result of an active stimulus of the en- 
vironment ? 
Subsidiary theories have been brought forward 1 to explain the 
evolution of monstrous reptiles, which were, by very reason of their 
specialised evolution unable to survive and are now merely indicated 
by those battered pages of history— the fossiliferous rocks. What 
1 Dendy. Momentum in Evolution. Report British Assoc. Adv. of Sc. 1911. 
