igog.] 



R. E. Li<OYD : Tlie Races of Indian Rats. 



97 



Fig. io. 



The conception which is in accordance with the Linnean no- 

 menclature may be illustrated by text-fig. lo, in which 

 the thick line represents the old species, the thin lines 

 the new species into which it has been divided, the 

 dotted lines representing the work of the future. This 

 is pleasingly simple and hopeful of finality, but it does 

 not seem to represent the way in which the animals 

 occur in nature. 

 The diagram, text- fig. ii, is perhaps more in accordance with 

 the actual occurrence. In this diagram the central thick line 



which represents the species Mus 

 rattus is supposed to consist of a 

 mass of tangled lines which are indi- 

 vidually visible as the terminal twigs 

 A. These represent the family 

 groups, the members of which show- 

 very slight differences from one 

 another, differences which are equi- 

 valent to the family likenesses of man. 

 These twigs are represented because 

 ten rats taken from any single house 

 in a town will often resemble one 

 another more closely than ten rats 

 taken haphazard from different 

 houses in the town. Some of these 

 groups are slightly removed from the 

 mean of the race, but all are not 

 so to an equal extent. The mean 

 of the race is represented by the 

 vertical line XX. Those groups 

 which in their characters diverge 

 widely from the mean are repre- 

 sented at a wider angle from the 

 parent stem. A well-marked sport 

 will therefore come oft' almost at a right angle. The many sports 

 and family groups which are unsuccessful are represented by short 

 lines, the few successful ones which have established a race are 

 indicated by longer and thicker lines, which themselves show side- 

 lines like the parent stem. A line ivhich does not deviate much from 

 the mean may be an old and powerful one: for example, Mus concolor 

 only differs in size from M . rattus, but it is a well-established line ; 

 its members extend throughout Burma and far be^^ond to the 

 south; it clearly shows its own side-lines, which are often of the 

 same kind as those of the parent stem. On the other hand a line 

 such as Mus blanfordi which deviates widely from the mean may 

 also be well established. 



Not every species could be accurately represented by this 

 diagram. The line of Mus decumanus would be shown with terminal 

 twigs but without any established side-lines, for in India the race 

 shows exactly the same fluctuating or normal variation as Mus 



