Now let us see how this may be answered. To my mind, in the 
first place there is nothing new in the case brought forward by Berg- 
son except the difficulty of a similar evolution occurring twice and 
in unrelated organisms. The eyes, however, are not alike in struc- 
ture. They certainly agree in being inverted, but even this inversion 
is different in type. Inversion occurs in other odd groups in the 
animal series and its isolated occurrence would suggest perhaps 
chance rather than design. A statement like the following: — “This 
inversion of the retinal layers occurs in all vertebrate animals but it 
is exceptional in the invertebrates 7 ’ is very misleading at the outset, 
for it suggests to the reader that the two groups — Vertebrata and 
Invertebrata — are of equal rank and their subdivisions too. 
We may regard similarity of structure in two invertebrate 
groups as surprising, but it would be much more extraordinary if 
we did not find similarity of structure in the different groups of the 
vertebrates, for they are much more closely related. In other de- 
tails beyond inversion there are no resemblances between the two 
eyes, and consequently any special deductions drawn from the sup- 
posed occurrence of two similar complicated structures are quite 
worthless. Johnstone grants the failure of Bergson’s argument in 
the case of the eye of Pecten, but suggests that a better case would 
be found in the convergent evolution of the teeth of “marsupials 
and some rodents.” This cannot possibly be accepted, for on almost 
any theory of evolution it is to be expected , as suggested above, that 
similar modifications in structure will be found in different Verte- 
brate groups owing to their close relationship. As a matter of fact 
the teeth of marsupials and rodents are homologous structures and 
any resemblance is a case of parallelism. Convergent evolution is 
a different thing altogether. 
We are thus left with Bergson’s general objection that Natural 
Selection could not have resulted in the evolution of such a complex 
structure as an eye. This very example was brought forward by 
Darwin himself and answered in the “Origin of Species.’’ Darwin 
writes : — “To suppose that the eye, with all its inimitable contrivances 
for adjusting the focus to different distances, for admitting different 
amounts of light, and for the correction of spherical and chromatic 
aberration, could have been formed by Natural Selection, seems, I 
freely confess, absurd in the highest possible degree. Yet reason 
tells me that if numerous gradations from a perfect and complex 
eye to one very imperfect and simple, each grade being useful to its 
possessor, can be shown to exist ; if, further, the eye does vary ever 
so slightly, and the variations be inherited, which is certainly the 
case, then the difficulty of believing that a perfect and complex eye 
could be formed by Natural Selection, though insuperable by our 
imagination, can hardly be considered real. He who will go thus 
far, if he find on finishing the treatise that large bodies of facts, 
otherwise inexplicable, can be explained by the theory of descent, 
ought not to hesitate to go further, and to admit that a structure 
