296 ANNUAL REPORT SMITHSONIAN INSTITUTION, 194 



Bats are the only mammals that truly fly, although there are rodents 

 in North America {Glaucomys)^ Africa {Anomalur-us and Idiurus), 

 and Asia (Pteromys and Scmropterus) that are called "flying squir- 

 rels," marsupials {Petaun(s) in Australia that are popularly known by 

 Ae same name, and insectivores {Galeopterus and Galeopithecus) in 

 the southern Asiatic regions that are usually called "flying lemurs." 

 In reality these mammals do not actually fly : they merely glide. Their 

 skins are a great deal larger than is necessary to envelop their bodies. 

 On each side the skin is extended outward in a fold to the wrists, 

 ankles, and hind feet. When the arms are spread forward and out- 

 ward and the hind legs are spread backward and outward, the con- 

 necting skin is stretched so that the animal becomes greatly flattened 

 and well adapted to gliding. The method is to climb to some fairly 

 high point, leap off and coast downward through the air. Just before 

 reaching the point at which it wishes to land, the animal turns upward 

 so as to check its flight. 



Bats, on the contrary, have true wings with a bone structure closely 

 resembling that of our arms and hands. Their fingers are enormously 

 elongated ; and stretched between the fingers and the arm bones and 

 extending back to the hind legs there is a thin, flexible fold of skin, 

 which in some groups of bats crosses the space between the hind legs 

 «7id includes part or all of the tail. With these remarkable wings bats 

 really fly. Most bats rest and sleep hanging head downward suspended 

 by their hind feet. Often the vertical surface on which the bat hangs 

 appears to us to be practically smooth ; but the small bats have such 

 sharp little hooked claws on their hind feet that they can hang up 

 on a roughness that we would scarcely detect. One that I had in my 

 home regularly hung up on a wall that was covered with paper that 

 was almost smooth. The method bats adopt to change from a condi- 

 tion of active flight to a perfectly quiet, restful position hanging hnad 

 downward, is interesting. I have observed that some bats at least 

 accomplish this by flying straight toward the wall until they are almost 

 touching it, then turning upward until they do actually touch the 

 wall, at the same time allowing themselves to fall sideways. Also, at 

 the same time, the claws attach themselves to the wall. This is done 

 so quickly that the human eye cannot follow the details of the animal's 

 action. When in this position, hanging head downward, a bat is 

 equally prepared to take off for another flight or to go to sleep. 



The sea bears or eared seals, most commonly known as "sealions" 

 {Otwria and Zalophus), and the fur seals [Callorhinus) have a fairly 

 flexible body and long flippers. . They hunch, sway, and flop along on 

 a flat surface so that they are frequently able to travel some distance 

 away from water on their bellies. Though greatly handicapped on 

 land, they are so adept in swimming that when in the water they 

 readily catch the fish on which they prey. 



