RECAPITULATION. 489 



living bodies of 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 

 detect3d. 



The complex and little known laws governing the pro- 

 duction of varieties are the same, as far as we can judge, 

 with the laws which have governed the production of dis- 

 tinct 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 con- 

 siderable 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, correlated variation seems to 

 have played an important part, so that when one part haa 

 been modified other parts have been necessarially modified. 

 With both varieties and species, reversions to long-lost 

 characters occasionally occur. How inexplicable on the 

 theory of creation is the occasional aj)pearance of stripes 

 on the shoulders and legs of the several species of the 

 horse-genus and of their hybrids! How simply is this 

 fact explained if we believe that these species are all de- 

 scended from a striped progenitor, in the same manner as 

 the several domestic breeds of the pigeon are descended 

 from the blue and barred rock-pigeon! 



On the ordiuary view of each species having been inde- 

 pendently created, why should specific characters, or those 

 by which the species of the same genus differ from each 

 other, be more variable than generic characters in which 

 they all agree? Why, for instance, should the color of a 

 flower be more likely to vary in any one species of a genus, 

 if the other species possess differently colored flowers, than 

 if all possessed the same colored flowers? If species are 

 only well-marked varieties, of which the characters have 



