418 AFFINITIES CONNECTING 



It should be observed that the process of imitation prob- 

 ably never commenced between forms widely dissimilar in 

 color. But, starting with species already somewhat like each 

 other, the closest resemblance, if beneficial, could readily be 

 gained by the above means, and if the imitated form was 

 subsequently and gradually modified through any agency, 

 the imitating form would be led along the same track, and 

 thus be altered to almost any extent, so that it might ulti- 

 mately assume an appearance or coloring wholly unlike that 

 of the other members of the family to which it belonged. 

 There is, however, some difficulty on this head, for it is 

 necessary to suppose in some cases that ancient members 

 belonging to several distinct groups, before they had diverged 

 to their present extent, accidentally resembled a member of 

 another and protected group in a sufficient degree to afford 

 some slight protection, this having given the basis for the 

 subsequent acquisition of the most perfect resemblance. 



ON THE NATURE OF THE AFFINITIES CONNECTING ORGANIC 



BEINGS. 



As the modified descendants of dominant species, belong- 

 ing to the larger genera, tend to inherit the advantages 

 which made the groups to which they belong large and their 

 parents dominant, they are almost sure to spread widely, 

 and to seize on more and more places in the economy of 

 nature. The larger and more dominant groups within each 

 class thus tend to go on increasing in size, and they conse- 

 quently supplant many smaller and feebler groups. Thus, 

 we can account for the fact that all organisms, recent and 

 extinct, are included under a few great orders and under still 

 fewer classes. As showing how few the higher groups are 

 in number, and how widely they are spread thoughout the 

 world, the fact is striking that the discovery of Australia 

 lias not added an insect belonging to a new class, and that 

 in the vegetable kingdom, as I learn from Dr. Hooker, it has 

 added only two or three families of small size. 



In the chapter on geological succession I attempted to 

 show, on the principle of each group having generally 

 diverged much in character during the long-continued pro- 

 cess of modification, how it is that the more ancient forms 

 of life often present characters in some degree intermediate 

 between existing groups. As some few of the old and inter- 

 mediate forms have transmitted to the present day descend- 



