NO. 1695. MOUSE DEER OF RHIO-LINGA ARCHIPELAGO— MILLER. 



Allusion to the uniformity of environment under which the mouse 

 deer exist has already been made. The geographic distribution of 

 the various forms is a further indication that the characters of the 

 species can not be explained as the result of local conditions. Linga 

 and Singkep are only 7 miles apart, but the napu of the former has 

 retained the primitive color pattern, while that of the latter is well 

 advanced toward the dark extreme. The species representing inter- 

 mediate stages are found 400 and 500 miles away, on the coasts of 

 the Malay Peninsula and west Sumatra. Similarly the phase that 

 lies between the Sinkep form and the extreme represented by that 

 of Kunder and (xreat Karimon occurs in the North Natuna Islands, 

 at a distance of 300 miles, and on Balabac, more than twice as 

 far away. On the other hand, the islands of Great Karimon and 

 Bulang, within 25 miles of each other, are inhabited, respectively, by 

 the most extreme black form and brown form now known. 



The only conclusion that seems justified is that the Tragulus napu 

 group consists of a series of local species whose color pattern, prob- 

 ably for some physiological reason, is varying along tw^o main lines 

 of divergence, both of which are independent of external conditions 

 as ordinarily understood. Each series is equally incapable of ex- 

 planation by the hypotheses of Lamarck, Darwin, or De Vries. On 

 the larger land masses such changes as may be taking place are uni- 

 form over wide areas and relatively slow, while in the regions wiiich, 

 by submergence, have become divided into small land areas separated 

 by water the changes are irregular and rapid, though progressing on 

 different islands at a very unequal rate.® 



"A somewhat parallel series of color changes in the African monkeys of the 

 genus Colohus has recently been described (Lydekker, Proc. Zool. Soc. I.iondon, 

 vol. 2. 1905. pp. 325-329). 



