100 THE SENSES OF ANIMALS 



and it is well known that blood from a wounded animal 

 will be detected from afar by these voracious fishes. It is 

 unlikely that the average student will be able to see this for 

 himself, but the fact is well established. Those who go in for 

 shark fishing pour some blood from an animal into the sea 

 in order to attract their quarry, and anyone lucky enough to 

 witness the way in which the sharks arrive will not be likely 

 to forget the experience. 



Reptiles 



The sense of smell is most marked in snakes and lizards, 

 though tortoises, turtles, and crocodiles also use their olfac- 

 tory organs. If you are a lucky field worker — and believe 

 me luck plays a great part in outdoor observations — you 

 may be able to see a snake following a scent trail, or a lizard 

 protruding its tongue before seizing some item of food. 



I remember one incident I witnessed not so many years 

 ago which showed how an adder could follow the scent trail 

 left by a field vole. The vole had been struck by the snake, 

 but not so effectively as to immobilize it completely. As I 

 was leading a natural history society's outing at the time, 

 several members were able to share in this interesting occur- 

 rence. We were walking along a path through some open 

 woodland, when I saw a sudden movement in a small clear- 

 ing not more than six yards from where we were. An adder 

 had just struck at a field vole and it still had it in its mouth, 

 when I drew the attention of the others to it. 



Our approach disturbed the adder, which made off 

 quickly, leaving the vole where it was. The vole, after a 

 second or two, crawled slowly into some undergrowth in the 

 opposite direction from that taken by the snake. I told my 

 companions to remain still for a while and then sit quietly 

 awaiting the adder's return, which I was sure would be 

 before long. In due course, the adder appeared, and with 

 its tongue flickering in and out very swiftly, it literally cast 

 around until it picked up the scent of the vole when it took 

 exactly the same route into the undergrowth. 



On another similar occasion, I saw an adder crawling 

 along, quite clearly following scent. As I watched, its 



