ANIMAL BEHAVIOR — WALKER 305 



back the next year to the exact spot that they started from the year 

 before. We know practically nothing as to what guides birds and 

 mammals on these long migrations; but we can readily observe in 

 many animals the painstaking investigation that they make of their 

 surroundings, obviously with the intention of familiarizing them- 

 selves with their immediate environs. 



A pet kangaroo rat that was given the run of our apartment for a 

 period of about 2 weeks selected the space beneath the mechanical re- 

 frigerator for her abode. Whenever she thought danger threatened 

 she would immediately retreat there. At other times she would ex- 

 plore around the apartment. If we remained quiet she would ven- 

 ture close to us. After about 2 weeks of this freedom she was kept 

 in a cage from which she was occasionally removed for little outings ; 

 however, she did not have another opportunity to utilize the space 

 beneath the refrigerator. But one day about a year later, when she 

 was again left free on the floor, she made persistent efforts to get 

 into the kitchen where the refrigerator was located, thus obviously 

 showing that her memory of the home she formerly used had re- 

 mained with her for at least a year. 



USES OF HANDS, FEET, TAILS, AND TEETH 



As "necessity is the mother of invention," it has naturally led ani- 

 mals to utilize their hands, feet, tails, and teeth in many effective ways. 

 The tails of horses, cattle, and a number of other animals are val- 

 uable in dislodging insect pests. In other mammals, such as the kan- 

 garoos {Macropus) and the jumping rodents, it is important as a 

 balancing organ and is sometimes used as a spare hind leg to make 

 a tripod to sit on. With the Old World monkeys the tail appears to 

 be largely an ornament, although it is useful in helping the animals to 

 keep their balance when leaping. Among the cats it is useful for 

 the expression of emotions; and it also assists the animals in right- 

 ing and balancing themselves when leaping or falling. Those cats 

 that have long and fairly bushy tails use them as muffs to help keep 

 their feet and noses warm. 



The binturongs (Arctictis) of the southern Asiatic region and the 

 pangolins {Manis, Smutsia, and related genera) of southern Asia and 

 Africa, also the North American opossum, the South American porcu- 

 pines (Coendou), and a few other animals use the tail mainly to 

 steady themselves by wrapping it around a limb, or to let themselves 

 down gradually when descending. Some of the American monkeys 

 use the tail regularly in this manner, the most noteworthy of these 

 animals being the spider monkeys (Ateles). The underside of the 

 tip of the spider monkey's tail is naked like a fingertip. This makes it 

 a good grasping organ. If an object is beyond the reach of the very long 



