Masterpieces of Science 



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 continual variations in the colour, 

 form and structure of all animals, has 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 variations both of 

 colour, form, structure, and instinct or habit, 

 must have occurred to produce the perfect 

 adaptation we now behold. All these are known 

 90 



