226 Letters, Announcements, ^c. 



soit aux ailes, soit aux sous-caudales. II est de la taille du 

 P. xanthospila. Si vous le jugez a propos^ vous pouvez 

 inserer cette note dans la correspondence de ^Flbis/ 



Votre tout devoue, 



P. M. Heude, S. J. 



Cambridge, Mass., 

 March 5, 1883. 



Sirs, — I have read with much interest Mr. Seebohm^s 

 paper in 'The Ibis' (Oct. 1882, pp. 546-550) ''on the 

 Interbreeding of Birds/' and while agreeing with him that 

 " the interbreeding of birds supposed to be specifically dis- 

 tinct " is a subject entitled to careful consideration, I cannot 

 see therein the complete explanation of "incipient species/' 

 or "subspecies/' he seems to find in it (?. c. p. 548). For 

 instance, I do not see how it can possibly explain the gradual 

 intergradation between the widely diverse forms of a species 

 often found occupying respectively the northern and southern 

 borders of the breeding-range of the species of which they 

 are unquestionably only extreme phases. To make my point 

 clear, I will cite a single case out of the many well known to 

 American ornithologists. Our common Partridge [Ortyx 

 virginianus) has a latitudinal range extending from Massachu- 

 setts to the southern point of Florida, throughout which area 

 it is an abundant and permanent resident. The South- Florida 

 birds, compaired with those from Massachusetts, are from 

 one fourth to one third smaller, with bills not only relatively, 

 but absolutely much larger, the whole plumage in general 

 effect many shades darker especially on the ventral surface, 

 where the transverse bars are greatly broadened at the ex- 

 pense of the alternating white interspaces. These differences 

 combine to give to the two forms strikingly diverse aspects, 

 the differences being as great and as easily defined as is often 

 the case among perfectly distinct though allied congeneric 

 species. If we knew only these two phases of the species in 

 question we could view them in no other light than as per- 

 fectly " segregated " species. But between these forms there 

 is every possible intergradation — a gradual passage of one 



