644 CHIROPTERA. 



some frugivorous. and some [Desmodus, Diyhylla) suck the 

 blood of other mammals. When at rest they hang suspended 

 by the claws of one or both legs, head downwards. On the 

 ground they rest with the knees directed upwards, and move 

 in a shuffling manner, pushing themselves along by their feet 

 which are rotated forwards and inwards, and[liauling themselves 

 forwards by the claws on tlieir thumbs. Many of them hiber- 

 nate, and in some at least the sexual season is separated by a 

 considerable interval from that of ovulation and conception 

 (see p. 517). The sexes appear frequently to live apart except 

 in the breeding season. 



They are nearly cosmopolitan in distribution,* There are 

 about 520 species and 95 genera of living forms. The earliest 

 fossil Chiroptera, which are from the Upper Eocene, show all 

 the features of specialisation of the order. Remains of about 

 6 genera and 35 species have been discovered, all belonging to 

 existing families. 



Such are the principal characters of the Chiroptera. It is 

 clear that they are a very sharply defined group with many 

 peculiar features, and the diversity of structure within the 

 group cannot be said to be very great. Formerly, on account 

 of the usual number of their upper incisors, the position of the 

 mammae, the pendent penis, the placental characters and the 

 form of the uterus they were included amongst the Primates ; 

 but there can be very little doubt that their real affinities are 

 with the Insectivora, 



The following details may be added to the foregoing account. 



The nose-leaves are found in the Hhivoloj^hidae, the Nycieridae and the 

 Phyllostomidae. They are folds of the skin at the margins of the nostrils, 

 are richly supplied with nerves (mainly derived from the nasal branch 

 of the trigeminal), and contain many sweat and sebaceous glands, which 

 maintain their surfaces in a soft and highly sensitive condition. There 

 can be no doi;bt that they are highly developed organs of touch, and are 

 one of the principal means by which their possessors are able to feel objects 

 without touching them, as bats are undoubtedly able to do. But this 

 function must also be discharged by other organs ; for the power of 

 avoiding obstacles in the dark is, as was shown by Spallanzani's experi- 

 ments, possessed by bats without a nose-leaf. These organs are pro- 

 bably the patagium, and the pinna of the ear which is remarkably de- 

 veloped in bats. The pinna is always large, and in seme species its length 



* Dobson, op. cit., states that they have not been found in Iceland, 

 St. Helena, the Galapagos Archipelago, Kerguelen Island, and the L9W 

 Archipelago. 



