VARIETIES OF RABBITS. 143 



tissues. For example, we find great differences in the 

 number of vertebrae and ribs, in the size and shape of the 

 gaps in the breast-bones, in the size and shape of the merry- 

 thought, in the lower jaw, in the facial bones, etc. In short, 

 the bony skeleton, which morphologists consider a very 

 permanent part of the body, and which never varies to such 

 an extent as the external parts — shows such great changes, 

 that many races of pigeons might be described as special 

 genera, and this would doubtless be done if all these different 

 forms had been found in a wild and natural state. 



How far the differences of the races of pigeons have been 

 carried is best shown by the fact that all pigeon breeders 

 are unanimously of opinion that each peculiar or specially 

 marked race of pigeons must be derived from a correspond- 

 ing wild original species. It is true every one assumes a 

 different number of original species. Yet Darwin has most 

 convincingly and acutely proved that all these pigeons, 

 without exception, must be derived from a single wild 

 primary species — from the blue rock-pigeon {Columha livia.) 

 In like manner, it can be proved of most of the domestic 

 animals and cultivated plants, that all the different races 

 are descendants of a single original wild species which has 

 been brought by man into a cultivated condition. 



An example similar to that of the domestic pigeons is fur- 

 nished among mammals by our tame rabbit. All zoologists, 

 without exception, have long considered it proved that all 

 its races and varieties are descended from the common wild 

 rabbit, that is, from a single primary species. And yet the 

 extreme forms of these races differ to such a degree from 

 one another, that every zoologist, if he met with them in a 

 wild state, would unhesitatingly designate them not only as 



