Form of the Nutcracker. 237 



the latter presenting the curious anomaly of having an inter- 

 rupted area of distribution. For this anomaly there is, 

 however, obvious and sufficient cause. The Northern forms 

 range from Scandinavia to Kamtschatka, but the range of 

 the Southern forms is interrupted by the plateau of the Hima- 

 layas and tlic desert of Mongolia, half lying in temperate 

 Europe and the British Islands,, and the other half in North 

 China and Japan. The Northern and the Southern races of 

 the Nuthatch, Sitta ccesia and S. casia uralensis ; of the 

 Marsh Tit, Parus palustris and P. palustris baicalensis ; of 

 the Magpie, Pica caudata and P. caudata leucoptera ; and of 

 the Hazel Grouse, Tetrao bonasia and T. honasia septentrio- 

 nuUs, are examples of the second kind of subspecific form. 

 In some of these cases the West European form is not abso- 

 lutely identical with the North Chinese race, and there are 

 cases in which tlie former intergrades with the Siberian race, 

 whilst the latter is not known to do so, as, for example, the 

 Great Spotted Woodpecker. Picus major is connected by a 

 series of intermediate forms with P. major cissa, but the 

 intermediate forms between the latter and its Chinese re- 

 presentative P. cabanisi, and its Japanese ally P.japonicus, 

 have died out or have not yet been discovered. The Northern 

 and Southern races appear to be climatic, the Siberian forms 

 of widely distinct genera being uniformly whiter than the 

 more southern races ; but how the climate affects the colour, 

 or what peculiarity of the climate is prepotent — the duration 

 of sunshine, the degree of cold, or the amount of rainfall — 

 is a mystery. One fact, however, appears to be without ex- 

 ception : the maximum of w^hiteness is not reached, as it 

 apparently ought to be, in the extreme north of Siberia, hut 

 in Kamtschatka, twenty degrees further south. The Kamt- 

 schatkan foims of the Nuthatch, Sitta albifrons ; of the 

 Marsh Tit, Parus kamtschatkensis ; of the Bullfinch, Pyrrhula 

 kamtschatka ; and of the Magpie, Pica kamtschatica, have 

 all been described as distinct, on the ground of their extreme 

 whiteness 



There are many other species of birds which may be re- 

 garded as residents in the Palsearctic Region, and of which 



