Masterpieces of Science 



caterpillars; or at other such cases. The wonder 

 indeed, is, on the theory of natural selection, that 

 more cases of the want of absolute perfection 

 have not been detected. 



The complex and little known laws governing 

 production of varieties are the same, as far as we 

 can judge, with the laws which have governed 

 the production of distinct species. In both 

 cases physical conditions seem to have produced 

 some direct and definite effect, but how much we 

 cannot say. Thus, when varieties enter any new 

 station, they occasionally assume some of the 

 characters proper to the species of that station. 

 With both varieties and species, use and disuse 

 seem to have produced a considerable effect; 

 for it is impossible to resist this conclusion when 

 we look, for instance, at the logger-headed duck, 

 which has wings incapable of flight, in nearly 

 the same condition as in the domestic duck; or 

 when we look at the burrowing tucu-tucu, which 

 is occasionally blind, and then at certain moles, 

 which are habitually blind and have their eyes 

 covered with skin; or when we look at the blind 

 animals inhabiting the dark caves of America 

 and Europe. With varieties and species, cor- 

 related variation seems to have played an im- 

 portant part, so that when one part has been 

 modified other parts have been necessarily modi- 

 fied. With both varieties and species, reversions 

 to long-lost characters occasionally occur. How 

 inexplicable on the theory of creation is the 

 occasional appearance of stripes on the shoulders 



