306 ANNUAL REPORT SMIl'HSONIAN INSTITUTION, 1940 



arms of a spider monkey, the animal "will sometimes back up as near 

 to it as possible, then reach out and grasp it with the tail tip. 



A good example of the manner in which the tai] is useful as a bal- 

 ancing organ or to check the animal when it is leaping is shown in the 

 picture of the douroucouli or night monkey (Aotus) of the Central 

 American region (pi. 16). On a few occasions I had noticed that 

 when these monkeys leaped onto a limb their tails swung forward 

 under the limb. However, the movement was so quick that I could 

 never be quite certain of the position the tail assumed. I could only 

 surmise that it was used to balance the animal. Wlien I took this 

 picture I was trying to photograph the monkey that is shown at the 

 right, but apparently an instant before I made the flash the monkey 

 at the left leaped onto the limb and checked his forward movement 

 by swinging his tail under the limb. His arrival caused the monkey 

 on the right to turn its head so quickly during the i/^o'o"Second expo- 

 sure that its face was slightly blurred. 



The pangolin uses its tail to wrap about itself to keep out enemies. 



The tails of whales and porpoises are the propellers that drive these 

 animals through the water. They work in a vertical plane instead 

 of horizontally like the tails of most fishes. 



The hands of gibbons and orangutans (Pongo) are long and slender 

 with the very small thumb placed far back. Thus, the hands are 

 better adapted to be used as flexible hooks than as grasping organs. 

 During their lives in the trees these animals use their hands in this 

 manner — that is, by hooking them over the limbs. This is of great 

 advantage to the gibbons in their flightlike swinging through the 

 trees. 



The feet of the gibbons, orangutans, and chimpanzees (Pan) are 

 fairly well adapted for grasping, the great toe being opposable to 

 the other toes. This permits them to use their feet in grasping limbs 

 or in carrying objects while they use their hands in swinging through 

 the trees. On one occasion I saw a young chimpanzee trying to carry 

 away all of its food at one trip. It had both its hands full and half 

 a head of lettuce grasped in one foot. 



The loosening and moving of earth, and in some cases the packing 

 of earth, plays so important a part in the lives of many animals that 

 they have developed considerable efficiency in the task. Most bur- 

 rowing animals do their digging with the forefeet, which are generally 

 rather large and are armed with short, straight, or slightly curved 

 claws well adapted for use as picks. They generally pull the earth 

 toward them and underneath them to a point where it can be reached 

 by the hind feet. These kick it backward. If they are working in- 

 side a burrow they generally turn around and go toward the entrance 

 pushing the loosened earth before them, using their front feet together 

 with their chests and throats as pushers while the hind feet supply the 



