VARIETIES OF RABBITS. 143 
tissues. For example, we find great differences in the 
number of vertebre 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 (Columba 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 
