Notices of New Books. 7599 



intermediate lines of species that have become extinct now on the 

 theory of advancement. It is somewhat plausible to assume that the 

 less useful ancestral forms have, in a regular progressive series, been 

 replaced by their improved progeny, A by B, B by C, C by D, D by IC, 

 and E by F ; but supposing we find the ancestor A, or its unaltered 

 descendants, still existing by the side of F andy, — and this is a case 

 abundantly and variously illustrated by the coteraporary existence of 

 organic beings of different degrees of organization, — we must assume, 

 first, that B had not a dominant advantage over A, or it would have ex- 

 tinguished A, and yet that it could bequeath to C a dominant advantage 

 over itself, parallel with the improved variation, which it did not inherit 

 with its own improved variation from A ; and, again, as we progress 

 upwards towards D and E, that the little steps of advantage accom- 

 panying the little steps of variation could individually effect the 

 extermination of the successive steps of variation without, in any 

 measure of their accumulation or divergence, summing up an advantage 

 over A. Then here we clearly establish the fact that dominant 

 advantage, or power of success in the struggle for existence, has not 

 an exact relation to other variations ; for instance, that those differ- 

 ences of structure upon which genera and species are based might go 

 on accumulating without that condition so absolutely essential to Mr. 

 Darwin's argument, that their power of dominion is correspondingly 

 increased; nay, some of the earlier forms may even retain, as in the 

 case of A, a slight measure of dominant advantage over its otherwise 

 advanced progeny ; lor we cannot reflect on the coexistence of organ- 

 isms of different height in the scale of nature without being convinced 

 of the fact, however securely those low in the scale may have been 

 saved by divergence of character from extinction in recent competition 

 with the higher, that there was a time at which they must, on the theory 

 of progression, have conquered forms genealogically and structurally 

 in advance of them, for they have outlived every gradation of the 

 assumed linlcs connecting them with higher organizations. 



It is difficult for the mind to picture the infinitely varied result of 

 Mr. Darwin's theory in the non-coincident operation of variation in 

 structure, and variation in power of dominion, as it must of necessity 

 involve every variety of gradation of character between organisms; but 

 in viewing the question as a matter of experience we do not see this, 

 nor a measure of it sufficient to account for the gradual mutation of 

 species. 



It is impossible, also, to imagine that such slight difierences of 

 dominant power as must of necessity separate the slight steps of 



