SIGHT FIELDWORK AND EXPERIMENTS 47 



explanation of some of the field observations I have carried 

 out more clear, I feel it is necessary to make brief references 

 to certain aspects of the optical mechanism of reptiles. 



It may be fairly stated that all reptiles are short-sighted 

 rather than long-sighted, but this does not mean that any- 

 thing which is some distance away — yards rather than feet 

 or inches — cannot be detected, though some degree of move- 

 ment is necessary. Reptiles, however, have apparatus for 

 accommodating to close vision since all of them must be able 

 to see their prey clearly when it is near at hand. 



It is certain that most reptiles, with the exception of croco- 

 diles and alligators, can see colours if only to a limited 

 extent. Any student can prove this for himself, as I have 

 done, with tortoises and some common species of lizards, 

 e.g. Viviparous Lizard, Sand Lizard, and Green Lizard. 



I have often demonstrated to interested friends that when 

 dandelions are in flower, if placed with some lettuce near 

 a tortoise, the tortoise will nearly always make straight for the 

 dandelion plant and eat the flower before it eats the foliage or 

 the lettuce. Curiously enough most of my tortoises have pre- 

 ferred dandelion and clover to lettuce, however succulent the 

 latter may appear. I have also watched my tortoises, when 

 placed on a lawn, move off on what might almost be de- 

 scribed as a tour of inspection. My lawn, I fear, often has 

 nearly as much clover and dandelion and plantain as it has 

 grass ; but this suits the tortoises even if it doesn't make for a 

 good lawn. 



However, the point here is that when the tortoises are 

 moving around they can be seen examining the plants in 

 front of them and selecting the ones they intend to eat. They 

 go first for clover, then dandelion and then plantain. They 

 can clearly recognize one plant from another; and if the 

 patch of lawn immediately in front of them contains no 

 clover they will move on until they detect some. Of course, 

 it must be admitted that the sense of smell is well developed 

 in tortoises, but from close observation I feel sure that when 

 covering a small area of ground in front of them it is by sight 

 that they find the desired food. 



No flower-bed containing pansies is safe from a tortoise, 

 but it will be seen that it is the yellow ones they go for first. 



