Vol. xliii.] 126 



what must be called, for want of better terms, " Sporadic 

 and Racial Hybrids." 



He said that, whereas these " Sporadic Hybrids " between 

 two well-defined species were very rare in Nature, the 

 "Kacial Hybrids" were exceedingly numerous — in fact, 

 they were pi'edominant — in the areas of contact between the 

 " subspecies " or " local races " in question. In the case of 

 some of these " Intergradational Series " the status was quite 

 clear, such as in the Fly River district of New Guinea be- 

 tween the two Paradiscea apoda forms and between Opopsitta 

 (^Ci/dopsitta auct.) godmani and Opopsitta cervicalis, for the 

 area inhabited by the intermediate forms is small and well 

 defined, and the series of individuals are the result of climatic 

 influence combined with interbreeding. This is also more 

 or less certainly evident in the cases of the Kingfishers Alcedo 

 athis atJiis and Alcedo atliis hengalensis and the Rollers Cora- 

 cias indica indica and Coracias indica a-ffinis ; but rather less 

 so in those of Indian Red- and Yellow-vented Bulbuls and 

 in the red- and yellow-rumped Rhamplwcoelus in Central 

 America. It is also evident in the North Asiatic examples of 

 the intersradations between Emheriza citrinella citrinella and 

 Emheriza citrinella leucocephala, and between the Eastern 

 form of Carduelis carduelis and Carduelis carduelis caniceps. 

 But we are faced with a different problem when we come 

 to the examples of the Crows Corvus corone corone and 

 Gcrvus corone cornix, the Thrushes Turdus naumanni euno- 

 mus and Turdus naumanni naumanni and between Turdus 

 ruficollis atrigularis and Turdus rujicollis ruJicolUs, the 

 Kaleege Pheasants Gennceus liorsjieldi and Genna^us nyctlie- 

 merus, and in North America between the " Red " and the 

 " Yellow Flickers " Colaptes, &c. Here the area inhabited 

 by the " Intergradational Series " is more extensive, often 

 ill-defined, and in ^the case of Kaleege Pheasants and 

 that of the Rock-Thrushes Monticola solitarius pandoo and 

 Monticola solitarius pliilippensis enjoying varied climatic 

 conditions. 



The extremely variable nature of the intermediate speci- 

 mens and the vast area inhabited by them in comparison 



