336 THE ZOOLOGIST. 



no pictures, and hence there is no power of visual discrimination 

 between objects. They probably recognize their right host by 

 the aid of organs of taste, and at any rate they are often able to 

 distinguish their host from closely allied species."* 



It is a long jump from a Leech to a Rhinoceros, but the 

 principle is the same, though the animals in a developmental 

 sense are so widely divided. Dr. Livingstone describes the 

 Ehinoceros as having such dimness of vision as to make it 

 charge past a man who has wounded it, if he stands perfectly 

 still, in the belief that its enemy is a tree. Dr. Livingstone, 

 however, adds that this imperfect sight probabl}' arises from 

 the horn being in the line of vision, " for the variety named 

 Kuahaoha, which has a straight horn directed downwards away 

 from that line, possesses acute eyesight, and is much more 

 wary."t Mr. Scott Elliot feels sure that the East African 

 Rhinoceros cannot see clearly for more than about fifty yards. I 

 Mr. Blanford, writing on the Abyssinian Rhinoceros, states that 

 *' they are easily eluded by turning, as they are not quick of 

 sight, and, like most mammals, they never look for enemies in 

 trees ; consequently a man two or three feet from the ground 

 will remain unnoticed by them if he keeps quiet. "§ Elephants 

 are reported to have a most defective power of sight, and, gener- 

 ally speaking, among mammals, as a rule, the world, as known 

 by their senses, is probabl)^ if we judge by vision alone, a 

 much more circumscribed one than that cognized by ourselves. 

 With other senses much more developed, and with the addition 

 of some of which we are totally ignorant, nature may be to them 

 revealed beyond our imagination. 



According to Dr. Giinther, fishes, in the range of their vision 

 and acuteness of sight, are very inferior to the higher classes of 

 vertebrates ; yet, at the same time, it is evident that they per- 

 ceive their prey or approaching danger for a considerable dis- 

 tance ; and it would appear that the visual powers of a Perioph- 

 thalmus, when hunting insects on mud-flats of the tropical coasts, 



'•= "Animal Behaviour," Biol. Lect. Marine Biol. Lab, Wood's Holl, 

 Mass. 1898, p. 293. 



I ' Miss. Trav. and Research in S. Africa,' p. 136. 

 I ' A Naturalist in Mid-Africa,' p. 247. 

 § ' Obs. Geol. and Zool. Abyssinia,' p. 248. 



