Common American Deer 251 



too small to enable me to form any decided opinion respecting the degree of 

 persistency of modification in the above-mentioned forms. Mr. Allen 1 has 

 conclusively proved that a decrease in size and characteristic development 

 takes place in all mammals, the centre of whose area of distribution is in 

 North America, as they spread southwards ; and, so far as the materials at my 

 command enable me to judge, I think it probable that the characters upon 

 which Gariacus /eucurus, C. mexicanus, C. savannarum, and C. peruvianas have 

 been established as species may be in large measure the result of this law." 



So far as specimens in the British Museum are concerned, the question 

 scarcely admits of a more decisive answer now than then. There can, 

 however, be no question but that all these forms are modifications of what 

 is essentially one type of animal, and they are accordingly here regarded as 

 sub-species rather than species ; an opinion shared by Mr. Rhoads, so far at 

 least as the Mexican form is concerned, and adopted by Mr. Caton for most, 

 and by Mr. A. Gordon Cameron for all the modifications. With regard to 

 their relationship and distribution Dr. P. Matschie writes as follows : — 

 " The two other kinds of Mazama deer found in South America are suffi- 

 ciently well distinguished from Cariacus peruvianas ; C. savannarum^ which 

 probably inhabits the whole extent of the Orinoco area, is pure grayish 

 brown with white speckling ; C. gymnotis, from the Magdalena River dis- 

 trict, yellowish brown with grayer speckling. To the northwards, in 

 Central America, C. nemoralis replaces C. gymnotis ; then follows in Yucatan 

 and South Mexico C. toltecus, C. mexicanus in Texas and Mexico, C. 

 leucurus in the Western, and C. virginianus in the Eastern United States." 



Although several previous writers have referred to the decrease in bodily 

 size and the diminution of the antlers in the members of this group as they 

 are traced from north to south, they do not appear to have noticed two 

 other features. These are a gradual darkening, and the tendency to the 

 assumption of a permanently dark coat {gymnotis and peruviamts) , and also to 

 the disappearance of the metatarsal gland and tuft, which become rudi- 

 mentary in nemora/is, and are quite lost in to/tecus, gymnotis, and peruvianus. 

 Both these are undoubtedly specialised peculiarities, the former being an 

 example of that tendency to blackness in many animals inhabiting humid, 

 and especially warm regions, to which reference has already been made 

 in the introduction. Glands are frequently found in animals living in 



1 Bull. U.S. Survey, 1876, p. 304. 



