HIGH SCHOOL ZOOLOGY. 183 



up into projecting I'ays ; in the other genera, Scalops and Scapamis, 

 the- Common and Hairy -tailed Moles, the snout is simply pointed. 



The other families are confined to the Old World ; their typical genera 

 are Erinaceua, the European hedge-hog, a terrestrial form iu which the 

 hairs are converted into stout spines ; it protects itself by rolling itself 

 into a ball, and thus causing the spines to diverge from each other. In 

 another family, to which the Centetes of Madagascar belongs, the spines 

 are replaced by bristles, which, with the pointed snout and strong lower 

 canines, give the creature some resemblance to a miniature pig. The 

 Malayan genus Tupaja and its allies are arboreal insectivores mth the 

 soft fur and habits of squirrels, and, in the same region, a singular genus, 

 GaleopitUecns, is to be met with, provided with a patagium like our 

 flying squirrels. It is the representative of an independent family, as 

 is also thfi African MacrosceVuhs, marked by the length of the hind 

 limbs, like the Jerboa, and occurring, like it, in rocky and desert regions. 



37. The chief contrast between the Insectivora and Rodentia 

 is ill the nature of the food, and the difference in structure and 

 habit brought about thereby. Nowhere is the difference in 

 structure more evident than in ttie dentition, where the incisoi's 

 aie reduced in number, grow from persistent pulps, and 

 acquire a chisel-shaped edge, from having the enamel only on 

 the antei'ior surface. Generally the incisors are only i, but in 

 the hares and rabbits (Leims), there is a small tooth behind each 

 of the curved upper incisors ; the canines are always absent, and 

 the molars never tuberculate, but provided with transverse folds 

 of enamel. As in the Herbivora, the stomach is constricted into 

 cardiac and pyloric chambers, and each of these may have re- 

 cesses ; further, the alimentary canal is long in proportion to the 

 body. 



Nearly half of our N". American Mammalia are Eodents belonging to 

 seven families, the Leporidce, Hy-slrkhida, Muridce, Dipodidce, Geomy- 

 idee, Castur'uke, Schiridce. The first of these includes the hares and rab- 

 bits, and is sufficiently characterized by its dentition. The type of the 

 second is the Old World Porcupine {Hystrix), represented in N. America 

 by the common porcupine {Ercthizon). Both of these forms have spines, 

 which are more ettcient weapons of defence than those of the hedgehog, 



