92 THE PHYSICAL KINSHIP 



type than the sirenians. Whales have two limbs, 

 the hind-limbs having disappeared as a result of 

 the pre-eminent development of the tail. The 

 tails of whales and sirenians are flattened horizon- 

 tally, not vertically, as in fishes. 



Out of generalised forms of hoofed animals now 

 extinct developed the odd -toed and even -toed 

 races of existing ungulates. The original ungu- 

 lates had five hoofs on each foot, and were highly 

 generalised in their structure. From these original 

 five- toed forms have arisen the variously hoofed 

 and variously structured tribes of existing ungu- 

 lates : the five-toed elephant, the four-toed tapir 

 and hippopotamus, the three-toed rhinoceros, the 

 two -toed camel, sheep, swine, deer, antelope, 

 giraffe, and ox, and the one-toed horse and zebra. 



The carnivorous branch of the placental animals 

 came from the carnivorous branch of the mar- 

 supials. From early forms of carnivorous pla- 

 centals developed the ape-like lemurs and those 

 generalised forms of rapacious animals from which 

 arose the insect-eaters, the bats, and the true 

 carnivora. The seals represent a by-development 

 from the main line of the carnivora, a third defec- 

 tion, and a comparatively recent one, from land 

 faunas. Seals live at the meeting of the land and 

 the waters rather than in or on the waters, as do 

 the cetaceans and sirenians. They have retained 

 their fur and their four limbs, but have almost lost 

 their power of land locomotion by the conversion 

 of their feet into flippers. The two front-limbs of 

 seals are the only ones used as ordinary limbs are 



