575 



tomed to a new mode of figlitin^- vvliicli made them acquire antlers. 



Tliis vicariating development can be understood, without taking- 

 refuge to such an intricate correlation between upper tusks and 

 antlers, as Bölschr does, where he speai^s of a surplus of energy 

 of growth, set free by retardation in the development of tusks, and 

 manifesting itself in hypertrophic excrescences on the frontal bones. 



When we proceed in this course of thought, the question unvolun- 

 tarilj arises, if the far higher development of tusks in the male 

 sex of so many species of mammals might not be considered as 

 a support for the abovementioned hypothesis about the androgenic 

 origin of frontal appendages. The difference between the two pheno- 

 mena lies especially in the fact, that with canines moditied to tusks 

 or incisors prolonged into darts, only their stronger development 

 and differentiation need be ascribed to influences of sexual, especi- 

 ally male nature, while for horns and antlers also their first appear- 

 ance had to be traced to this same cause. But this does not exclude 

 that the tusks of P]lephants and ('etacea, the canines of so many 

 Apes, Carnivores and ungulates etc. tind their most plausible expla- 

 nation in the assumption, that in so far as they are lai'ger than the 

 other teeth and also differ in shape and position from the incisors 

 and molars, they may be considered as an acquisition of the male 

 sex, which afterwards passed to the female, but in reduced pro- 

 portion, and so to a certain extent again lost its monosexual character. 

 Especially the growth far over the limits of practical fitness may 

 be adduced as an argument for this hypothesis; we should only 

 remember the tusks of the Manunoth cui-led up in a complete circle, 

 the gigantic canines of the male walrus or the usually unilateral 

 dart of the male Narwhal. 



In this connection I should like to move the question whether the 

 uncouth tusks of the extinct Sabretoothed tiger (Machaii-odiis), might 

 not have formed a special attribute of the male sex, as beyond doubt 

 they were far from practical in defence as well as offence. Witli cer- 

 tainty this is the case with the Walrus. Also the upper canines of 

 the Babirussa, which perforate the upper lip, and are cuiled up 

 dorsally and backwards, give us a good example of hypertrophic 

 growth far beyond the limits of i-eal usefulness. 



Groningen, September 1918. 



