366 THE ZOOLOGIST. 



like the European, instead of slate as in all the other species. 

 Thus we find in this group a uniform graduation of variation as 

 we proceed further from the cradle of the race. 



A similar series of modifications may be traced in the 

 Chaffinch (Fringilla), which has been in like manner derived 

 from the North African F. spodiogena, and in which the extreme 

 variation is to be found in the westernmost islands of Palma and 

 Hierro. The Willow Wren, Phylloscopus trochilus, extremely 

 numerous and resident, has entirely changed its habits, though 

 not its plumage, and I have felt justified in distinguishing it as 

 P. fortunatus. In note and habits it is entirely different from 

 our bird, and though it builds a domed nest it is always near the 

 top of lofty trees, most frequently in palm-trees. The only 

 external difference from our bird consists in its paler tarsi and 

 more rounded wing, so that its power of flight is weaker, but, 

 were it not for the marked difference in its habits and voice, 

 I should have hesitated to differentiate it. In the Kestrel and 

 Great Spotted Woodpecker there are differences which suggest 

 incipient species, while the forests of the wooded western islands 

 yield two very peculiar Pigeons, differing entirely from each other 

 in their habits, both probably derived from our Wood Pigeon, 

 but even further removed from it than the Columba trocaz of 

 Madeira, and by their dark chestnut coloration, suggesting that 

 peculiar food, in this case the berries of the tree laurel, has its 

 full share in the differentiation of isolated forms. If we remember 

 the variability of the pigments in the food of birds, and the amount 

 absorbed and transferred to the skin and plumage, the variability 

 in the tints and patterns of many animals can be more readily 

 understood. 



One other bird deserves notice, the Caccabis, or Red-legged 

 Partridge, for here, and here alone, we have chronological data. 

 The Spaniards introduced Caccabis rufa into Canary, and 

 C. petrosa into Tenerife and Gomera, and they have never spread 

 from their respective localities. Now, both species, after a 

 residence of only 400 years, have become distinctly modified. 

 C. rufa was introduced into the Azores also, and changed exactly 

 in the same manner, so much so that Mr. Godman, some years 

 ago, in his ' Natural History of the Azores,' would have described 

 it as distinct, but that the only specimen he procured was in 

 moult and mutilated, and it now proves identical with the 



