390 RECAPITULATION. [CHAP. XV. 



the 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 detected. 



The complex and little known laws governing the 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 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 has been 

 modified other parts have been necessarily modified. 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 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 

 descended 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 ordinary view of each species having been independently 

 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 colour of a flower be more likely to vary in 

 any one species of a genus, if the other species possess differently 

 coloured flowers, than if all possessed the same coloured flowers? 

 If species are only well-marked varieties, of Avhich the characters 

 have become in a high degree permanent, we can understand this 

 fact ; for they have already varied since they branched off from a 

 common progenitor in certain characters, by which they have come 

 to be specifically distinct from each other ; therefore these same 

 characters would be more likely again to vary than the generic 

 characters which have been inherited without change for an 

 immense period. It is inexplicable on the theory of creation why 

 a part developed in a very unusual manner in one species alone of 

 a genus, and therefore, as we may naturally infer, of great inLport- 



