MAMMALS 73 



It is mentioned by Darwin that those species of seal in 

 which sexual differences are conspicuous are polygamous. 

 But as we have seen, the significance of this fact is that the 

 polygamous males fight more than the others. Polygamy 

 means the exclusive possession of several females, and the 

 exclusive possession of one female may, as in the case of the 

 moose deer, necessitate habitual fighting. The male cat and 

 the buck rabbit are not strictly monogamous, and they indulge 

 in occasional fights, but they use as weapons only the teeth 

 and claws which the female equally uses in ordinary life. 

 Sexual intercourse with these animals is promiscuous, and 

 therefore they do not fight so habitually as those who assume 

 the exclusive possession of the females. 



Cetacea. The most conspicuous instance of unisexual 

 characters in Cetacea is the single spiral tusk of the male 

 narwhal. This tusk is sometimes from 9 to 10 feet in 

 length, and is an enlarged, continually growing, canine. The 

 canine of the opposite side is usually about 10 inches long, 

 though occasionally both are equally developed. In the 

 female both are rudimentary. It is believed that the males 

 use these weapons in fighting together, but no information is 

 given by Darwin concerning the period of life at which they 

 develop, nor concerning the relations of the sexes in the 

 species. Male sperm whales fight with their heads and 

 jaws, and the head of the male is larger than that of the 

 female. 



Ungulata. Among the even-toed ruminating ungulates 

 secondary sexual characters are more strongly developed than 

 in any other group of Mammalia. The antlers of deer are, in 

 fact, among the most interesting and remarkable of such 

 characters. It is well known that these antlers are in reality 

 branched outgrowths of the frontal bones of the skull, and 

 their development in the common stag does not merely take 

 place once in each individual, but is repeated every year. 



