130 EVOLUTION IN THE PAST 



good-sized rhinoceroses, and they somewhat resembled those 

 creatures in appearance. Their skulls were adorned on the 

 forehead with a pair of small horns, whilst the greatly en- 

 larged nasal bones supplied a second pair of comparatively 

 huge dimensions. A good-sized Arsinoitherium was there- 

 fore an imposing figure. He certainly was the outcome of a 

 long course of evolution ; and was, indeed, at the end of it, 

 for his family is not known after this Period. As to his 

 ancestry zoologists as yet know little more than did the 

 creature himself. 



Some forms of primitive elephants were living in his 

 neighbourhood ; and Arsinoitherium may have enjoyed the 

 society of these fellow-vegetarians. But he stood out in 

 strange contrast with them. They were in the dawn of 

 their history : he was hasting to his setting. 



Other discoveries have been made in Egyptian strata 

 which show that some mammals had taken to an aquatic life, 

 after the manner of certain reptiles in earlier times. 



SIRENIA Some of these were " sea-cows " of primitive type, and 

 are represented to-day by the dugongs and manatees 

 (Eotherium, Eosiren Andrewsi). These pioneers seem to 

 have been related to the small, marsh-dwelling elephants ; 

 but they must long have quitted the original fold. In 

 possessing hind-limbs they presented a notable difference 

 from sea-cows now living. This difference, however, is not 

 to be wondered at ; for the appendages, indispensable to 

 their land-frequenting ancestors, must have been too well- 

 developed to dwindle away rapidly. Nor had the hind- 

 limbs in the next Period entirely disappeared. 



WHALES Other mammals that had taken to the water were toothed 

 much as the primitive carnivores, but resembled whales as 

 regards the skull (Protocetus). These creatures were rather 

 long in the neck ; but their bodies were assuming a fish-like 

 shape ; and their " arms " were probably being modified into 

 fins. The supersession of lungs by gills was not to be expected ; 

 for there was no dormant gill-apparatus to be aroused to 

 action. 



These creatures were followed during the Period by 

 similar forms : but these had undergone dental modifica- 



