20 BULLETIN NO. VII. 



during flight. The first finger may be reduced to a single 

 phalanx and the other digits may also be somewhat reduced 

 but they never coalesce as in birds. The thumb is commonly 

 furnished with a nail which frequently serves as a support 

 during the day-time or period of winter repose. The other 

 fingers are greatly elongated and are very strong and elastic, 

 Usually if a bat is brought down by a blow it will be found that 

 the humerus, or short bone of the arm. is broken while the 

 more slender phalanges are intact. 



The volatory apparatus, however, consists, besides the wing 

 of various other membranes, or rather continuations, of the 

 web above mentioned. The humeral portion is a triangular 

 gib-like membrane passing from the wrist to the sides of the 

 neck or shoulder, and is, in some species, pocket-like. There 

 is also a broad membrane passing posteriorly to the legs. This 

 web corresponds to that expansion of the skin which forms 

 a parachute by which flying squirrels "fly." Another portion, 

 the interfemoral membrane, connects the feet with each other. 

 The tail is ordinarily included in this membrane, but its apex 

 may extend beyond, or it may be entirely wanting. In some 

 species the leg is armed with long spurs homologous with the 

 cartilage upon the wrist of the flying squirrel which serve as 

 supports to the web. 



The form is various, but is uniformly plump with a short 

 neck and thick body. 



When not in motion the ensemble is bizarre and formless. 

 (See Fig. 1, heads of various bats. ) The smaller bats resemble 

 mice in their pelage and general appearance and are retaliative 

 and fierce when caught. 



The head is rendered remarkable by enormously expanded 

 ears, often provided with a large simple or lobed tragus which 

 serves as a sort of valve for closing the ear. In many species 

 the nose is also ornamented with extraordinary folds of skin, 

 which seem to be the seat of the delicate tactile sense for which 

 bats are distinguished. The eyes of bats are very small, and seem 

 adapted to the peculiar nocturnal habits of the animal, but are 

 supplemented by the senses of touch and hearing. In a room, 

 across which wires have been stretched in all directions, a bat 

 will fly freely without dashing against them even when the 

 eyes are destroyed or blindfolded. 



The volar membrane is itself very sensitive, being richly 

 supplied with nerves as well as bloodvessels. In the eye of 

 nocturnal animals, generally the spindle-shaped bodies in the 



