608 



MR. P. C. MITCHELL ON A FORMULA TO 



[Nov. 4, 



be drawn with four strokes of the pen thus indicates the regions in 

 their relative positions, fig. 1. 



Fig. 1. 



Nearctic. 



PaUearctic. 



Neotropical. 



Ethiopian. 



Oriental. 



Australian. 



The four subregions in each region except in the Nearctic 

 region He, in a general way, two to the north, two to the south, two 

 to the east, two to the west. In the Palsearctic region, for instance, 

 the Xorth-European and Siberian subregions are the northern pair ; 

 the Mediterranean and 3Ianchurian the southern pair ; the North- 

 European and Mediterranean are the western, the Siberian and 

 Maiicliurian the eastern subregions. If the subregions are numbered 

 thus : — 



North-European 1 



Mediterranean 2 



Siberian 3 



Manchurian 4 



and if the numbers be placed as indicated in figure 2, it will be seen 

 that the numbers are in the relative position of the regions they 

 denote. 



Fig. 2. 



1 

 2 



3 



4 



The numbers 1, 2, 3, 4 are placed in similar relative position in 

 the spaces corresponding to the other regions except the Nearctic, and 

 obviously represent subregions as in the following list : — 



Ethiopian Region 



Oriental 



1. West Africa. 



2. South Africa. 



3. East Africa. 



4. Madagascar. 



1. Hindostan. 



2. Ceylon. 



3. Indo-China. 



4. Indo-Malav. 



