68 THE SENSES OF ANIMALS 



to do without light but they can't do without oxygen ! So 

 see that your tank is not too small if you wish to cover it 

 with a light-proof box or with a blanket or other soft cover. The 

 reason why you must take this precaution is due to the fact 

 that these mammals use up their energy so quickly that 

 they must renew it by means of oxygen intake as well as 

 food. 



As to colour sight, it has already been stated that with 

 the exception of the anthropoid apes and probably some of 

 the monkeys as well, mammals do not have colour sight. 

 This has been well substantiated by dissection and examina- 

 tion of the eyes of dead specimens, and it is really a waste 

 of time to carry out experiments to prove what is already 

 established. The truth is that mammals, with the exception 

 of the kinds mentioned, have no use for colour sight and 

 nature seldom, if ever, endows a creature with a sense which 

 is of no practical use to it. 



