240 Canon Tristram on the Polar Origin of Life 



Texas. When on the verge of the tropics we seem to lose the 

 genus. 



The next most northerly groups of Woodpeckers are the 

 genus Gecinus on the European and East-Asiatic lines of 

 migration, and the genus Colaptes on the American line. 

 These grojips seem to have left the north before the Picinse, 

 and to have pushed further southwards. They vary still 

 more from the original type in their southerly migration, 

 especially when they penetrate into the Indian region, as in 

 such species as Gecinus mentalis and G.jmniceus. In the case 

 of Colaptes we have the instance of C. chilensis, the most diver- 

 gent and the least differentiated of the group, as if the direct 

 descendant of progenitors who, at a very early period, pushed 

 southward till they reached a climate similar to that of their 

 original home, and thus never became differentiated like those 

 which remained in warmer latitudes. Both Picus and 

 Gecinus reached the southern shores of the Mediterranean, 

 but never crossed the Saharan Ocean. 



All the other families of Woodpeckers, driven southward 

 long before the above-named had left the north, have become 

 more and more segregated, and can at once be classified into 

 the three great groups which have peopled the Indian, Ethi- 

 opian, and Neotropical regions. Why not one of them ever 

 crossed the mysterious dividing-line between Bali and Lom- 

 bock is a problem only to be solved when research shall have 

 revealed to us more accurate knowledge of the conformation of 

 the Indian and Australian areas during the Miocene epoch. 



The similarity of the fauna of Japan with that of Western 

 Europe has often been noted, and also the remarkable fact 

 of forms occurring in Japan which do not recur till we 

 reach the west of Europe, while there is no affinity with the 

 avifauna of America. Take as an instance Oijanopica. If 

 the Azure-winged Magpie had been wholly or partially circum- 

 polar, we could easily understand one party going down 

 Western Europe and halting in Spain, the other resting in 

 Japan. Of Pica, colonies seem to have started down the 

 routes of Europe and East Asia, and a third down the west 

 side of the Rocky Mountains, Avhile some selected the Nortli- 



