224 Proceedings of the Royal Physical Society. 



the two species. When we come to look at the secondaries, 

 we shall, however, find that in L. excubitor, the bars of their 

 outside webs are also white, so that two white patches or 

 bars are formed on the wings, whilst in L. major, there is no 

 white at the base of the outside webs of the secondaries, so 

 that only one white patch or bar is formed on the wing. 

 Some ornithologists have suggested that L. major is the 

 young of L. excuhitor, but nestlings of the latter species, in 

 which the wings are not even fully grown, show the two 

 white patches almost as distinct as adults. Further east 

 still, a third species occurs, X. leucopterus, in which the whole 

 of the inside web, and all except a narrow streak near the 

 centre of the feather adjoining the shaft of the outside web, 

 is white. The white at the base of the primaries also 

 extends to twice the distance that it does in the other two 

 species. Z. major breeds in Central Scandinavia, North 

 Ptussia, and across the whole of Siberia up to about lat. 60°. 

 X. excuhitor breeds in Europe south of lat. 50°, as far east 

 as Moscow, and L. leiicoptei^us in Turkestan and South Cen- 

 tral Siberia, as far east as Lake Baikal. 



But now comes the curious part of the history of these 

 birds. In the valley of the Yenisei, both L. major and 

 X. leucopterus are found, so far as we know perfectly distinct 

 species, which are too wide apart ever to interbreed, though 

 their geographical areas there overlap, and give them every 

 opportunity of doing so. It would appear, however, that the 

 intermediate form, X. excuhitor, is near enough to each of the 

 two extremes to interbreed with either of them, for in 

 Scandinavia and North West Eussia, where the geographical 

 areas of X. excuhitor and X. major impinge, every intermediate 

 form between them occurs ; and in South Eastern Eussia and 

 Western Turkestan, the white on the wings of the Grey Shrikes 

 gradually increases as you go eastward, so that in the interme- 

 diate localities between the eastern limit of true X. excuhitor 

 and the eastern limit of true X. leucopterios, a complete 

 series of intermediate forms between the two are obtainable. 



