IV. VERTEBRATA: MAMMALIA, CHIROPTERA. 637 



the rudimentary condition or occasional absence of the canines 

 (Talpa fjii. miny shrews ffff). There is great variability in 

 the matter of replacement of teeth; in the shrews, for instance, 

 the milk dentition is suppressed and 

 the second only is functional, while in 

 the hedgehog one incisor and one pre- 

 molar in each jaw, a second premolar 

 and the canine of the lower jaw func- 

 tion in both dentitions. In many re- FIG. 66i.-skuii of Sorex. (From 



,, . ,. Ludwig-Leunis.) 



spects the insectivores resemble the 



rodents : a clavicle is present ; there are usually five toes furnished 

 with claws; there is a uterus bicornis, often divided its whole 

 length, and discoidal placenta. 



Aside from the proboscis-like snout the insectivores resemble the 

 rodents in appearance, forming parallel groups to those of that order. 

 The ERINACID.E, or hedgehogs, of the Old World are spined like the porcu- 

 pines ; the SORICID.E, or shrews (Sorex,* Blarina*), are mouse-like, as are 

 the allied TALPID.E, or moles (Scalops,* Condylura,* star-nosed mole), 

 which burrow in the earth and have the eyes more or less rudimentary. 

 Some authors place here Galeopithecus of the East Indies, which has a 

 similar membrane and similar sailing powers as the flying squirrels. It 

 also presents resemblance to the bats and to the lemurs. The earliest 

 known insectivores date from the eocene. 



FIG. 662. Skeleton of bat. (After Brehm.) 



Order III. Chiroptera. 



The bats are the only mammals which actually fly, and this at 

 once characterizes them. The flying membrane (patagium) is a 

 thin fold of skin, richly supplied with nerves, which begins at the 



