600 r. s. lull variations or specific distinctions: which? 



Age Distinctions 



There is little difficulty, as a rule, in detecting relative age, especially 

 in mammals in which the teeth are preserved, but in certain instances, 

 notably among the camels and horses, tooth proportions change so much 

 that comparative measurements should be studied with great caution. 

 The development of crests on the skull, as in the adult male gorilla, is 

 conceivable as a response to increasing muscular power with maturity, as 

 well as alteration of jaw form, especially toward the muzzle, as old age 

 approaches. Badly worn teeth, especially in a carnivore, would certainly 

 imply a necessary dietary change, with a consequent muscular modifica- 

 tion, probably degeneration. 



To what extent age characters would modify the bodily skeleton, to the 

 confusion of the systematist, is not clear. 



Sex Distinctions 



In the modern mammal, these are seen not alone in pelage, which is, of 

 course, lost to the paleontologist, but in actual bodily changes aside from 

 differentiation of size — such, for instance, as the mighty shoulders of a 

 bull bison, which react not alone in muscle, but in bone as well. It may 

 readily be inferred that such must also have occurred among titanotheres 

 and other huge well armed beasts. 



Antlers and horns in the extinct deer and antelope are, of course, 

 readily recognized sex distinctions, as are doubtless the presence or degree 

 of development of tusklike canines and incisors ; but rarely, I think, does 

 one realize the extent of the mechanical reaction of the remainder of the 

 skull to the presence or absence of such structures. This was brought 

 before us in a very vivid and disquieting manner recently in the case of 

 two skulls of the Chinese water deer, Hydropotes inermis, in the Pea- 

 body Museum Osteological Collection — one a male, the other a female. 

 The former possesses great laniary canine tusks, whereas in the latter the 

 canines are very small, inwardly curved, and probably hardly penetrated 

 the gum. The animals were both fully adult, but the teeth of the male 

 show a somewhat greater degree of wear. 



The other skull distinctions follow: Length, male, 172 millimeters; 

 female, 154 millimeters: bizygomatic diameter, male, 74 millimeters; 

 female, 64.5 millimeters. 



The cheek teeth of the male are larger, especially the premolars, of 

 which P 2 is more complex, the mesostyle being more pronounced. The 

 molars are very- narrow in the female and there is no trace of the internal 



