448 Darwin, and after Darwin. 
far from being developed for the exclusive benefit of the larvae, it is 
easy to see that, allowing a tendency to gall-formation, natural 
selection would have developed galls exclusively for the benefit of the 
plants, so that they might suffer a minimum of harm from the unavoid- 
able attacks of insects. 
But here it may be questioned—have we proof that internal feeders 
tend to form galls? In answer to this I would point out that gall- 
formation is a peculiar feature, and cannot be expected to arise in 
every group of internal feeders. But I think we can afford sufficient 
proof that wherever it has arisen it has been preserved : and further, 
that even the highly complex forms of ga'ls are evolved from forms 
so simple that we hesitate to call them galls at all. 
The paper then proceeds to give a number of individtal cases. 
No doubt the principal objection to which Mr. Cockerell’s 
hypothesis is open is one that was pointed out by Herr Wet- 
terhan, viz. “the much greater facility afforded to the indirect 
action through insects, by the enormously more rapid succession 
of generations with the latter than with many of their vegetable 
hosts— oaks above all*.” This difficulty, however, Mr. Cockerell 
believes may be surmounted by the consideration that a growing 
plant need not be regarded as a single individual, but rather 
as an assemblage of such *, , 
Note C To PAGE 394. 
The only remarks that Mr. Wallace has to offcr on the 
pattern of colours, as distinguished from a mere dré/Ziancy of 
colour, are added as an afterthought suggested to him by the 
late Mr. Alfred Tylor’s book on Colouration of Animals and 
Plants (1886). But, in the first place, it appears to me that 
Mr. Wallace has formed an altogether extravagant estimate of the 
value of this work. For the object of the work is to show, 
“that diversified colouration follows the chief lines of structure, 
and changes at points, such as the joints, where function 
changes.” Now, in publishing this generalization, Mr. Tylor— 
who was not a naturalist—took only a very limited view of the 
! Entomologist, March, 1890. 2 Nature, vol. xli, p. 394. 
8 Lbid. vol. xli, pp. 559-500. 
