THE GROWTH OF GROUPS 87 



is also characteristic of several species. There is a 

 group of such rats in the Philippine and neighbouring 

 islands, which is spoken of collectively as the Xanthurus 

 group. They have received the specific names, xanthurus, 

 everetti, meyeri, celebensis, macleari, and luzonicus. If 

 the tail of one of the sports shown in Fig. 2 d be com- 

 pared with that of Mus macleari (illustrated in the pro- 

 ceedings of the Zoological Society for 1887), little difference 

 will be found between them. In both cases there is 

 complete loss of pigment from the whole circumference 

 of the tail in the terminal quarter of its length and the 

 change from the coloured to the colourless portions is 

 abrupt, so that whereas one of the tile-like scales may 

 contain the full amount of pigment, another in contact with 

 it may be devoid of pigment. If we are to believe that the 

 parti-coloured tail which is characteristic of the Xanthurus 

 group is a definite character, being represented both in 

 the germ and in the body of all animals of the group, 

 we can believe no less in the case of the two sports from 

 Amritzar. I have had the opportunity of comparing 

 the sports side by side with specimens of M. macleari. 

 It cannot be said that the character is exactly the same 

 in both. Thus, in the sports the white area invades the 

 pigmented area in an irregular manner on the ventral 

 surface but not on the dorsal surface or on the sides ; 

 but in macleari the change is sudden round the whole 

 circumference of the tail. Although, as regards this 

 character, the sports are slightly different from the 

 species (macleari) yet both the sports are alike ; the 

 white area invades the pigmented area in an irregular 

 manner on the ventral surface in both of them. We may 

 say, therefore, that the sports do not possess exactly the 



