﻿242 BRITISH FOSSIL CEPHALOPODA. 



observable in the Silurian period, at least. There are changes of fauna indeed, but 

 they are more or less gradual. The argument from the imperfection of the 

 geological record is of little avail ; for the number of individuals found, which range 

 themselves round specific centres, even counting all those of one locality as a single 

 individual, is sufficient to render the probability that such centres exist very much 

 greater than that the series from which these terms were selected at random should 

 be uniform. 



The great defect of the theory of natural selection is that it leaves the original 

 variation, which is the basis of the whole, to chance ; chance variations are not 

 likely to lead to any law, yet there are several well-marked laws in the progress of 

 the various forms of life. The part which it has effectually performed is to show 

 how variations of the individual may produce permanent changes in the species, 

 and thus to break down the idea of the fixity and independence of the latter. The 

 chance variations were appealed to in the proof as illustrations, and have been 

 assumed to be the kind actually operating, but there is not the slightest evidence that 

 an indefinite change from species to species may be brought about by this kind of 

 variation. We are perhaps as yet too dazzled by the brilliancy of the theory to 

 perceive its inadequacy as a complete account of life, or to place it as one link only 

 in the chain of explanation. 



The whole of the facts of embryology teach us to look to the development of the 

 individual from the ovum to the perfect animal as the summing up of the history of 

 the species in its evolution from the lowest forms, and to my mind the only adequate 

 account of the evolution of the whole animal kingdom is derived from the same 

 analogy more fully carried out. Only superficial differences can be perceived in 

 the ova of very different animals, yet each goes forward to its perfection along 

 perfectly marked lines. If, for example, it be the ovum of a bird, there is no 

 attempt (as far as we can tell) to try various kinds of development, as of a reptile 

 or of a mammal, and to select the birds as the fittest ; but the ovum contains in 

 its essence all the future features of the adult, to the paintings on its plumage 

 and the pattern of its comb. Chance variations and natural selection have no 

 place in these larger matters, though minor details, say of colour, may depend 

 on the relative size of capillaries, itself depending on the chance development 

 of the cells. This individual development along predetermined lines is due, 

 according to the theory of natural selection, to heredity — or the property 

 which the ovum possesses of reproducing not only the character of the parents, 

 but the history of their evolution. It is admitted, therefore, that the ovum 

 has some properties, however derived, which cause it to develop in a certain 

 way, and this would be equally true if we were (as we are) ignorant of their 

 mode of derivation. 



