274 HIPPOPOTAMUS 



jaw, and they were distinguished as a genus Hexaprotoclon, con- 

 trasting with Tetraprotodon, until intermediate conditions were 

 observed. Ghoero-psis, as akeady observed, was a still further 

 reduction of the tetraprotodont type. The molars (the formula is 

 Pm I M 1) when worn show a double trefoil pattern. The 

 orbital cavity is encircled by bone. As with many other aquatic 

 mammals the kidneys are lobulated. 



Fig. 140. — Hippopotamus. Hi_ppopotamus ampliihius. x ^„. 



A very singular fact about the Hippopotamus is the pro- 

 duction of a " bloody sweat," a carmine-coloured secretion, con- 

 taining small crystals and corpuscles, from the skin. This 

 coloured fluid has of course nothing to do with blood.^ 



The animal grows to a length of at any rate 14 feet. The 

 limbs and the tail are short. Like other aquatic animals the 

 nostrils are on the surface of the head, and can be closed when 

 the animal is under water. When it reaches the surface of the 

 water after a prolonged immersion, it spouts like a Whale. Sir 

 Samuel Baker says that ten minutes is the longest time that the 

 Hippopotamus can remain below the water. It is frequently a 

 dangerous animal to encounter, as it will capsize boats, and even 

 bite large pieces out of their bottoms ; with its huge teeth it 



' Tomes, Froc. Zool. Soc. 1850, p. 160. 



