386 AFFINITIES CONNECTING Cuap. XIII. 



tliis variety, from its rcseinl)lancc to a flourishing aiul little-per- 

 secuted kind, has a better chance of escaping' destruction from 

 predacious birds and insects, and is consequently oftener pre- 

 served ; " the less ];)erfect degrees of resemblance being gener- 

 ation after generation eliminated, and only the others left to 

 ]')ropagate their kind." So that here we have an excellent il- 

 lustration of natural selection. 



Mr, Wallace has recently described several equally striking 

 cases of mimicry in the Lepidoptera of the Malay Archipelago, 

 and other instances could be given with other orders of insects. 

 Mr. Wallace has also described one case of mimicry among 

 birds, but we have no such cases Avith the larger quadrupeds. 

 Tlie much greater fi-equency of mimicry with insects than with 

 other animals, is probably the consequence of their small size ; 

 insects cannot defend themselves, excepting indeed the kinds 

 that sting, and I have never heard of an instance of these 

 mocking other insects, though they are mocked ; insects can- 

 not escape by flight from the larger animals ; hence they are 

 reduced, like most weak creatures, to trickery and dissimula- 

 tion. 



But to return to more ordinary cases of analogical resem- 

 l:)lance : as members of distinct classes have often been adapted 

 by successive slight modifications to live under nearly similar 

 circumstances — to inhabit, for instance, the three elements of 

 land, air, and water — we can perhaps understand how it is that 

 a numerical parallelism has sometimes been observed between 

 the sub-groups in distinct classes. A naturalist, struck by a 

 ])arallelism of this nature in any one class, by arbitrarily rais- 

 ing or sinking the value of the groups in other classes (and all 

 our experience shows that their valuation is as j'et arbitrary) 

 could easily extend the parallelism over a wide range ; and 

 thus the septenary, quinary, quaternary, and ternary classifica- 

 tions have probably arisen. 



0)1 tlic N'ature of the Affinities connecting Organic be- 

 ings. — As the modified descendants of dominant species, be- 

 longing to the larger genera, tend to inherit the advantages 

 which made the groups to which they belong large aud 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 

 ttMid to go on increasing in size ; and they consecjjiently sup- 

 j>lant many smaller and feebler groups. Thus wc can account 

 for the fact that a]l organisms, recent and extinct, are included 



