310 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1940 



reason to suppose that they can see in the total darkness prevailing 

 in their burrows and in many places that they regularly frequent. 

 They become accustomed to following a wall or the base of a tree; 

 and their whiskers tell them that they are keeping just a whisker's 

 length away from it. If a change in the surroundings has been 

 made while they were away, they at once detect it, or if an object has 

 been placed in the path and their forward-extended whiskers touch 

 it, they have such control of their movements that, ordinarily, they 

 will stop or turn before they actually hit the object. Furthermore, 

 they have such exceptional powers of scent that they may be able to 

 detect the newly placed object or the disturbed condition before they 

 come in contact with it. Possibly they may even Icnow by counting 

 a given number of steps that they have traversed a given distance 

 in a certain direction and that the time has come to change their 

 course. 



The fact that any species of animal has survived the numerous 

 hazards that have beset its kind down through the ages shows that 

 it must have become efficient enough in its mode of life to have es- 

 caped destruction by famines, floods, droughts, diseases, fires, and 

 predatory animals. We know from the records of the gi'eat number 

 of animals now found as fossils that many species were not able to 

 survive. Sometimes the geologists and paleontologists have been able 

 to reach a conclusion as to why these species became extinct; in 

 other instances they are still at a loss for an explanation. It is ob- 

 vious, however, that the animals living today are descended from 

 ancestors that were able to cope, through the ages, with nature's great 

 array of hazards and problems ; in other words that the efficient ones 

 survived and the inefficient ones succumbed. 



PLAY AND EXERCISE 



Most people have, of course, witnessed the play of kittens and pup- 

 pies and that of some other young animals. But play is not limited 

 to the very young of only a few kinds. It is obviously enjoyed by 

 so many different creatures that there can be no doubt that practi- 

 cally all animals play. Young carnivores when playing with others 

 of their kind leam how to stalk, attack, and overpower their prey. 

 This can easily be witnessed by watching kittens at play. Squirrels, 

 even adults, plainly engage in play when they chase each other about 

 and obviously have grand times. 



I have often noticed that my pet grasshopper mouse, "Ony," 

 which has freedom on my desk almost every evening, frequently will 

 make unnecessaiy movements that plainly show his exuberantly 

 good spirits. By flipping a piece of string at him I induce him to 

 play with the string and pull at it much as a dog pulls at a rope. 



