710 Mrs. Rose Haig Thomas on [Ibis, 



XXXIX. — Hybrids 0/ Geun8eus/?'o»i jXatiiral and Artificial 

 Crosses showing similar Pattern and Intergrading . Bj' 

 Mrs. Rose Haig Thomas, M.B.O.U. 



In a paper entitled " A Revision of the Genus Gennteus'" 

 (Journal of the Bombay Natural History Society, xxiii. 

 1915, p. 658), Mr. Stuart Baker draws attention to a con-, 

 tiuuous natural hybridization taking place between G. hors- 

 jieldi of j.\ssam, the " Black Kalij,'' and G. nycthemerus, 

 the Silver Pheasant, inhabitinir the neiohbourino- Northern 

 Shan States, and to ils geographical distribution over those 

 countries and Burma, Tenasserim, and Siam. Convinced 

 of the hybrid nature of many specimens the author reduces 

 the number of subspecies to simpler figures ; he points out 

 the large number of birds shot within the triangle contain- 

 ing Assam, Northern Shan States, and Tenasserim, which, 

 though given the rank of subspecies, are undoubtedly 

 hybrids, and further states that round every area in which 

 these subspecies (discontinuous hybrids) are found, a zone of 

 unnamed intermediates exists, and that, where the differing 

 forms of Gennceus ^' horsjieldi''' and ^'"nycthemerus''' are close 

 neighbours and " the physical geographical change abrupt," 

 the hybrid intermediates are so numerous and so infinitely 

 graded that none deserve sub-specitic rank. The geneticist 

 might consider these to be F. 1 in constant generation by 

 continuous intercrossing and the few fixed discontinuous 

 hybrids (subspecies) either F. 2 or F. 3 inter se, or cross- 

 backs. At any rate, Mr. Stuart Baker's interesting investi- 

 gations call attention to an extensive district where natural 

 intercrossing between two widely differing species of a genus 

 is occurring and evolving, either by loss of, or linkage of, 

 or by re-combination of factors, new forms, some of them 

 constant and heritable. 



To whatever cause the author may attribute the variations 

 of these new forms, he abandons the task of separating the 

 numerous intergrades, and classifies only the fixed forms as 

 subspecies. The interest of Mr. Stuart Baker's revision 

 has been much increased by the issue of a paper in 

 ' Genetics' (vol. vi. July 1921, pp. 366-383) by Mr. J. C. 



