64 



ISLAND LIFE. 



[part t. 



of mammalia. It will be interesting therefore to examine the 

 few cases on record, as we shall thereby obtain additional know- 

 ledge of the steps and processes by which the distribution of 

 varieties and species has been brought about. 



Discontinuity of the Area of Parus palustris. — Mr. Seebohm, 

 who has travelled and collected in Europe, Siberia, and India, 

 and possesses extensive and accurate knowledge of Palsearctic 

 birds, has recently called attention to the varieties and sub- 

 species of the marsh tit (Parus pahistris), of which he has ex- 

 amined numerous specimens ranging from England to Japan.^ 

 The curious point is that those of Southern Europe and of 

 China are exactly alike, while all over Siberia a very distinct 

 form occurs, the sub-species P. borealis. In Japan and Kam- 

 schatka other varieties are found, which have been named 

 respectively P. japonicus and P. camschatkensis. Now it all 

 depends upon these forms being classed as sub-species or as 

 true species whether this is or is not a case of discontinuous 

 specific distribution. If Parus horealis is a distinct species from 

 Parus palustris, as it is reckoned in Gray's Hand List of Birds, 

 and also in Sharpe and Dresser's Birds of Europe, then Parus 

 jpalustris has a most remarkable discontinuous distribution, as 

 shown in the accompanying map, one portion of its area com- 

 prising Central and South Europe and Asia Minor, the other 

 an undefined tract in Northern China, the two portions being 

 thus situated in about the same latitude and having a very 

 similar climate, but with a distance of about 4,000 miles be- 

 tween them. If, however, these two forms are reckoned as 

 sub-species only, then the area of the species becomes con- 

 tinuous, while only one of its varieties or sub-species has a 

 discontinuous area. It is a curious fact that P. palustris and 

 P. horealis are found together in Southern Scandinavia and in 

 some parts of Central Europe, and are said to differ somewhat 

 in their note and their habits, as well as in colouration. 



Discontinuity of Eniberiza schceniclus. — The other case is that 

 of our reed bunting (Emheriza schceniclus) , which ranges over 

 almost all Europe and Western Asia as far as the Yenesai valley 

 and North-west India. It is then replaced by another smaller 

 1 See Ihh, 1879, p. 32. 



