64 ON THE ORIGIN AND [CHAP. 



not come within the popular ken. " La larve," 

 Quatrefages, "n'est qu'un ernbryon a vie indepen- 

 dante." 1 Those naturalists who accept in any form 

 the theory of evolution, consider that " the embryonal 

 state of each species reproduces more or less completely 

 the form and structure of its less modified progeni- 

 tors." 2 "Each organism," says Herbert Spencer, 3 

 " exhibits within a short space of time a series of 

 changes which, when supposed to occupy a period 

 indefinitely great, and to go on in ' various ways 

 instead of one way, give us a tolerably clear concep- 

 tion of organic evolution in general." 



The naturalists of the older school do not, as 

 Darwin and Fritz Muller have already pointed out, 

 dispute these facts, though they explain them in a dif- 

 ferent manner generally by the existence of a sup- 

 posed tendency to diverge from an original type. 

 Thus Johannes Muller says, " The idea of develop- 

 ment is not that of mere increase of size, but that of 

 progress from what is not yet distinguished, but which 

 potentially contains the distinction in itself, to the 

 actually distinct. It is clear that the less an organ is 

 developed, so much the more does it approach the 

 type, and that during its development it acquires 

 more and more peculiarities. The types discovered 

 by comparative anatomy and developmental history 

 must therefore agree." And again, "Whatsis true in 

 this idea is, that every embryo at first bears only the 



1 Metamorphoses de THomme et des Ammaux, p. 133. See also 

 Carpenter, Principles of Physiology. 1851, p. 389. 



2 Darwin, Origin of Species, 4th ed. p. 532. 



3 Principles of Biology, vi. p. 349. j 



