in PROTECTIVE RESEMBLANCES AMONG ANIMALS 49 



case the fittest will survive, and a race will be eventually 

 produced adapted to the conditions in which it lives. 



We have here an illustration of the simple and effectual 

 means by which animals are brought into harmony with the 

 rest of nature. That slight amount of variability in every 

 species, which we often look upon as something accidental or 

 abnormal, or so insignificant as to be hardly worthy of notice, 

 is yet the foundation of all those wonderful and harmonious 

 resemblances which play such an important part in the 

 economy of nature. Variation is generally very small in 

 amount, 1 but it is all that is required, because the change in 

 the external conditions to which an animal is subject is 

 generally very slow and intermittent. When these changes 

 have taken place too rapidly, the result has often been the 

 extinction of species ; but the general rule is, that climatal 

 and geological changes go on slowly, and the slight but con- 

 tinual variations in the colour, form, and structure of all 

 animals have furnished individuals adapted to these changes, 

 and who have become the progenitors of modified races. 

 Rapid multiplication, incessant slight variation, and survival 

 of the fittest these are the laws which ever keep the organic 

 world in harmony with the inorganic, and with itself. These 

 are the laws which we believe have produced all the cases of 

 protective resemblance already adduced, as well as those still 

 more curious examples we have yet to bring before our 

 readers. 



It must always be borne in mind that the more wonderful 

 examples, in which there is not only a general but a special 

 resemblance as in the walking leaf, the mossy phasma, and 

 the leaf -winged butterfly represent those few instances in 

 which the process of modification has been going on during 

 an immense series of generations. They all occur in the 

 tropics, where the conditions of existence are the most 

 favourable, and where climatic changes have for long periods 

 been hardly perceptible. In most of them favourable varia- 

 tions both of colour, form, structure, and instinct or habit, 

 must have occurred to produce the perfect adaptation we now 

 behold. All these are known to vary, and favourable varia- 



1 Later research has shown that variation is more frequent and of greater 

 amouiit than at first supposed. See Darwinism, chap. iii. 

 E 



