390 THE BIOLOGY OF BIRDS 



factor, which is what true blending implies. It is necessary 

 to have further data in regard to the next generation. 



The results of crossing different species of birds seem 

 often to point to what may be described as " blending." 

 Thus John C. Philipps reports (1915) crosses between pintail 

 and mallard, Anas tristis and mallard, and Black East India 

 duck and mallard, in which one of the outstanding results 

 was that many characters, apparently clear-cut and 

 antagonistic, do not segregate clearly. On almost every 

 feather region the minutest details of pattern and colour 

 show the influence of both parental races. It is otherwise 

 in hybrids between distantly related forms. Some of the 

 particular results of species-hybridisation are interesting. 

 Thus if only one of the species is sex- dimorphic, a more 

 primitive type of male plumage occurs in the hybrids. 

 Hybrids between mallard and black duck showed a condition 

 closely resembling eclipse or summer plumage. 



{d) It very occasionally happens that the ofi"spring 

 exhibits a feature not seen in either of its parents, but 

 characteristic of a distant ancestor. This is described as 

 reversionary inheritance or harking back, and it may be 

 illustrated by the case of a Rock-dove type suddenly appear- 

 ing as the result of an unfortunate cross between two dis- 

 crepant breeds of pigeon. Thus Professor Cossar Ewart 

 (1899) reports an experiment in which a pure white fantail 

 cock pigeon, of old-established breed, which in colour had 

 proved itself prepotent over a blue pouter, was mated with a 

 cross previously made between an " owl " and an " arch- 

 angel," which was far more of an " owl " than an " arch- 

 angel." The result was a couple of birds, one of which 

 resembled the Shetland rock-pigeon and the other the blue 

 rock of India. Not only in colour (slaty-blue), but in shape, 

 attitude, and movements, there was an almost complete 

 reversion to the form which is believed to be ancestral to all 

 the domestic breeds of pigeon. The fact was there, and 

 what was seen may be described as a reversion. It does not 

 follow, however, that what occurred was a re-awakening or 

 re-habilitation of long dormant hereditary traits characteristic 



