Chat. XXVIII. CONCLUDING EEMARKS. 403 



have been highly abnormal in comparison with all their 

 congeners. They maintain that certain species, which 

 formerly existed, have become extinct, or are now unknown, 

 although formerly known. The assumption of so much 

 recent extinction is no difficulty in their eyes ; for they do 

 not judge of its probability by the facility or difficulty of ihe 

 extinction of other closely-allied wild forms. Lastly, tKey 

 often ignore the whole subject of geographical distribution as 

 completely as if it were the result of chance. 



Although from the reasons just assigned it is often difficult 

 to judge accurately of the amount of change which our 

 domesticated productions have undergone, yet this can be 

 ascertained in the cases in which all the breeds are known 

 to be descended from a single species,— as with the pigeon, 

 duck, rabbit, and almost certainly with the fowl ; and by the 

 aid of analogy this can be judged of to a certain extent with 

 domesticated animals descended from several wild stocks. It 

 is impossible to read the details given in the earlier chapters 

 and in many published works, or to visit our various ex- 

 hibitions, without being deeply impressed with the extreme 

 variability of our domesticated animals and cultivated plants. 

 No part of the organisation escapes the tendency to vary. 

 The variations generally affect parts of small vital or physio- 

 logical importance, but so it is with the differences which 

 exist between closely-allied species. In these unimportant 

 characters there is often a greater difference between the 

 breeds of the same species than between the natural species 

 of the same genus, as Isidore Geoffroy has shown to be the 

 case with size, and as is often the case with the colour, 

 texture, form, &c, of the hair, feathers, horns, and other 

 dermal appendages. 



It has often been asserted that important parts never vary 

 under domestication, but this is a complete error. Look at 

 the skull of the pig in any one of the highly improved breeds, 

 with the occipital condyles and other parts greatly modified ; 

 or look at that of the niata ox. Or, again, in the several 

 breeds of the rabbit, observe the elongated skull, with the 

 differently shaped occipital foramen, atlas, and other cervical 

 vertebrae. The whole shape of the brain, together with the 



