22 BULLETIN NO. VII. 



roosts at night. In such resorts, which are ordinarily used 

 during summer as sleeping places during the day, immense 

 quantities of guano are deposited which become valuable as 

 nitre supplies. Thus the insignificant bat plays no insignifi- 

 cant part in the warlike preparations of militant nations, as 

 the nitre so secured is an essential factor in gunpowder. 

 During hibernation and daily sleep, bats are in danger from 

 prowling animals which creep upon them when at rest; while 

 during their hawking excursions after insects they frequently 

 fall victim to the nocturnal birds of prey. 



Bats may be reckoned among the beneficial animals, as their 

 food consists almost exclusively of insects in temperate regions. 

 They are aptly compared to swallows, as their benevolent in- 

 tent and their graceful motions are both similar. The bats of 

 the tropics are larger and do not content themselves with in- 

 sects and other small arthropods. Various fruits form a wel- 

 come contingent, if not the staple of the diet, while still others 

 are bloodthirsty enemies of large animals which they attack 

 stealthily, sucking the blood painlessly and escape unperceived. 



The hair of bats may be distinguished from that of other 

 mammals by its peculiar microscopical structure. The fine fur 

 is a refuge for many parasites of various sorts. It remains to 

 mention the anatomical peculiarities of the group. 



The dentition is extremely variable, but in general resembles 

 that of the Insectivora. The greatest diversities are found 

 between the f rugivorous and insectivorous bats. The number 

 of teeth varies from 24 to 38. The statements of various auth- 

 ors vary greatly as to the number of teeth a fact caused by 

 their deciduous character, particularly of the incisors and pre- 

 molars. The molars have two or three points which are vari- 

 ously arranged and those of opposite teeth fit between each 

 other. The incisors are small and above are often arranged 

 in oblique series not meeting in the median line. The milk 

 dentition is quite different from the permanent. 



Most species produce but a single young at a birth or at most 

 two. The mother hangs by the thumbs, it is said, and the 

 young are dropped into a pocket formed by the incurved tail with 

 the membranes attached. Here they remain clinging for a day 

 to peculiar processes between the thighs, or at once clamber up 

 to the two pectoral mammae. Although northern species mate 

 ordinarily in Autumn, eggs are not fertilized until Spring, 

 when impregnation takes place. The placenta is disc -like and 

 the uterus has two cornua. The penis is pendulous. 



