272 STUDIES, SCIENTIFIC AND SOCIAL chap. 



magpie is found in North-eastern Asia from Shanghai to 

 Pekin and the Amoor, as well as in Japan ; and these 

 countries reproduce the hot summers and the cold winters, 

 the rugged mountains and the sheltered valleys of Spain, 

 while both areas are subject to the influence of the 

 vicinity of the ocean in an almost equal degree. 



Before going further we must guard against a 

 misconception as to the progressive rise and decay of 

 species, genera, and higher groups. It is not maintained 

 that this will always take place uninterruptedly or 

 continuously. On the contrary, it is certain that the 

 decay of a group may run its course for a time, and then, 

 owing to changed conditions, may be checked, and even 

 be changed into a new growth and development. Hence 

 arise those isolated groups, which yet, by their abundance 

 in species and the considerable area they occupy, show 

 that they are in a flourishing condition — of which the 

 tanagers in South America (Tanagridae), the broadbills 

 (Eurylsemidse) of Asia, and the colies of Africa (Coliidse), 

 may serve as examples. When an extensive group is in 

 process of extinction, it may become broken up into many 

 isolated portions, sometimes in juxtaposition to each 

 obher, sometimes separated in remote parts of the globe. 

 Changes of conditions, whether physical or organic, may 

 favour first one, then another, of these portions, or the 

 same portion may be subject to alternate phases of 

 progression and decay several times repeated. How can 

 we wonder that the final result of such complex processes, 

 whose general nature we can understand but whose 

 details it is impossible for us to trace, should often lead 

 to anomalies in geographical distribution ? And when 

 we consider that these processes have been often 

 intensified and further complicated by geographical 

 mutations, and by those forced migrations induced by the 

 climatal changes which culminated in the glacial epoch, 

 the wonder rather is that we can account for so much, 

 than that there should be matters of detail which we 

 cannot explain. 



It is clear, then, that the case of the Little Blue Magpie 

 of Spain and its close ally in Eastern Asia is simply an 



