CHORDATA 395 



digit of the fore limb is tipped with a claw, and in some 'Dais 

 there is a claw on the second digit as well. All five digits of the 

 hind foot are clawed. The body is usually covered with short, 

 soft fur, except in one group, which is practically naked. 

 There are two mammae on the thorax, and in some spe» 

 these are thought to be functional in the male as well as in the 

 female ; the penis is pendant, and there is no scrotum. The 

 dentition is complete. All the special sense organs except sight 

 are highly developed, especially the sense of touch. Of the 

 internal anatomy we need merely note that the bones are very 

 light, and a keel is developed on the sternum for the attachment 

 of the pectoral muscles used in flight, very much like that found 

 in birds. Many of them have a strong, musky odor, due to the 



Fig. 384. Synotus barbastellits, a bat. (After Vogt and Sprecht, from Parker and 



Hasvvell's Manual.) 



secretion of certain glands in the skin. The bats are nocturnal 

 animals, generally gregarious, but the sexes live apart, as a 

 rule, except during the breeding season ; during the daytime 

 they remain in dark places, suspended by their claws, head 

 downward (Fig. 385). Many of them hibernate during the 

 winter months. They feed chiefly on insects ; some live entirely 

 on fruits, and others suck the blood of warm-blooded animals. 

 Fossils are rare in this order. 



The bats comprise over four hundred species, and may be 

 separated into two groups. In the one belong the majority of 

 the larger bats, some seventy species ; they feed exclusively 

 on fruits and have claws on both the first and second digits of 

 the fore limb. The tail, when present, is not included in the 

 interfemoral membrane, but lies below it. These bats, known 



