202 DOMESTIC PIGEOXS. Chap. VI. 



were all coloured blue, and had the wing-bars and other cha- 

 racteristic marks of C. livia, — a supposition which is highly im- 

 probable, as besides this one species no existing member of the 

 Columbidae presents these combined characters ; and it would 

 not be possible to find any other instance of several species iden- 

 tical in plumage, yet as different in important points of structure 

 as are pouters, fantails, carriers, tumblers, &c. Or lastly, we 

 may assume that all the races, whether descended from G. livia 

 or from several aboriginal species, although they have been bred 

 with so much care and are so highly valued by fanciers, have 

 all been crossed within a dozen or score of generations with 

 C. livia, and have thus acquired their tendency to produce blue 

 birds with the several characteristic marks. I have said that it 

 must be assumed that each race has been crossed with C. livia 

 within a dozen, or, at the utmost, within a score of generations ;. 

 for there is no reason to believe that crossed offspring ever revert 

 to one of their ancestors when removed by a greater number of 

 generations. In a breed which has been crossed only once, the 

 tendency to reversion will naturally become less and less in the 

 succeeding generations, as in each there will be less and less of 

 the blood of the foreign breed ; but when there has been no 

 cross with a distinct breed, and there is a tendency in both 

 parents to revert to some long-lost character, this tendency, for 

 all that we can see to the contrary, may be transmitted undimi- 

 nished for an indefinite number of generations. These two 

 distinct cases of reversion are often confounded together by those 

 who have written on inheritance. 



Considering, on the one hand, the improbability of the three 

 assumptions which have just been discussed, and, on the other 

 hand, how simply the facts are explained on the principle of 

 reversion, we may conclude that the occasional appearance in 

 all the races, both when purely bred and more especially when 

 crossed, of blue birds, sometimes chequered, with double wing- 

 t>ars, with white or blue croups, with a bar at the end of 

 the tail, and with the outer tail-feathers edged with white, 

 affords an argument of the greatest weight in favour of the 

 view that all are descended from Columba livia, including under 

 this name the three or four wild varieties or sub-species before 

 enumerated. 



