HY THE REV. CANON TRISTRAM. 31 



have been able to collect facts and specimens which illustrate 

 the modification and extinction of specific forms and the results 

 of isolation. For instance, it has been shewn that the Blue 

 Titmouse, which was formerly identified with that of North 

 Africa, is really distinct, and has been modified, so that four 

 perfectly distinct forms are found in the Archipelago ; one, very 

 closely allied to the Algerian form, in the two eastern islands ; 

 another, inhabiting the three central islands of Canary, Teneriffe, 

 and Gomera; another, very distinct (with white instead of yellow 

 and black underparts), confined to the Island of Palma ; and a 

 fourth, equally marked, having the back green instead of blue, 

 restricted to a single bird found in the Island of Hierro. In a 

 similar way the Chaffinch of Europe, which in l^orth Africa is 

 represented by a very distinct form, of different coloration and 

 considerably larger size, is, in the Atlantic Islands, further and 

 most distinctly modified. There is considerable general affinity 

 between the races of Madeira, the Azores, and the different 

 islands of the Canary group, but each easily recognizable ; and, 

 as in the case of the Titmouse, the birds of the three central 

 islands, Canary, Teneriffe, and Gomera, are identical, while 

 that of Palma is distinct, and that of Hierro intermediate be- 

 tween the Palma and the Teneriffe species. In the two eastern 

 islands, which are without forests, the Chaffinch is absent. But 

 in Teneriffe there is also another very distinct Chaffinch, much 

 larger than the others, of an uniform slaty blue, and of very 

 different habits, entirely confined to the Pine forests round the 

 Peak of Teneriffe, about 5,000 feet above the sea. Again, the 

 Gold-Crest, which is identical through all the islands, is distinct 

 from the European bird in some slight characters, in which it 

 resembles the Eire-Crests, while the Gold-Crest of Madeira is 

 entirely distinct. But the most remarkable feature of the or- 

 nithology of these islands is the existence of three very distinct 

 species of Pigeon, distantly allied to our "Wood Pigeon ; one in 

 Madeira; a second in the Laurel forests of Teneriffe, Gomera, 

 and Palma, and which formerly no doubt existed in Canaria 

 before the destruction of the forest ; and a third confined to the 

 precipitous ledges of the forests of Gomera and Palma, but not 



