On Species &• Varieties in Birds. i39 



wines and tail, and forms which as one goes east pass into the 

 Amirican Lanius borealis, so that it becomes a question 

 whether one should treat all as one species, or split them up 

 into several. I have here a considerable series of specimens 

 from different parts of Europe, Asia, -d North America 

 which will at a glance show the extreme difficulty there is in 

 definin- what is a species and what a variety. I may also 

 name with regard to these Shrikes that the varieties appear to 

 be solely climatic, and do not at all arise from the interbreeding 



of allied forms. . , ■ ^r -p^^A 



Amongst Flycatchers are found two species of Pied 



Flycatchers in Europe, Muscicapa atncapilla and msa- 



capa collaris, the latter diff-ering only (but constantly) m 



having a white collar. Our Redbreasted Flycatcher, which 



throughout Europe is not subject to any variation is/eplaced 



in eastern Asia by Muscicapa luteola which has only the throat 



and not the breast red, and in some parts of India and Ceylon 



by Muscicapa hyperythra which has the red on the breast 



bordered with rich velvety black. Muscicapa parvathongh 



an extremely rare British bird, has been once known o breed 



with us, and I believe that the first announcement of this lact 



was made in this room by Mr. J. Flower, one of our members 



Our common Swallow, Hirundo rustica, is replaced in north 



east Africa by a very deeply coloured allied species Htrundo 



^avignii, and in eastern Asia one finds ^iorm (Htr undo 



tytleri), which is half way between our bird and the widely 



distributed American species Hirundo horreorum. 



Amongst the FringiUidce one finds several mstances of 

 climatic forms, which, by constant isolation, have become 

 distinct species, as for instance Serinus hortulanus which is 

 replaced by Serinus canonicus in the east and by Sermus 

 canarins on the Atlantic islands. Ligurinus chloris in southern 

 climes becomes much brighter coloured, but cannot be divided 

 into two species, but Fringilla celebs is replaced m north 

 Africa by Fringilla spodiogcna, and in the Azores by Fringilla 



^"xhe Redpolls are a most puzzling group, for, although they 

 may be fairly sub-divided into four species, Lmota rufescens 

 Linota Unarm, Linota exilipes, and Linota hornemanni, yet 

 one finds so many forms between Linota linaria and Ltnota 

 .exilipes that one is almost inclined to term the latter a species 

 still in the process of differentiation. _ 



Of our common Bullfinch we have two forms in Europe, 

 Pyrrhula Europcea in the west, and Pyrrhula major m the east ; 

 but on the Atlantic islands one finds a very distinct species, 

 Pyrrhula murina ; and in eastern Asia two, one Pyrrhula 

 orientalis which has only the throat red in the male, and 



