688 ROUEXTIA. 



called ivory. This latter portion wears away much more rapidly than 

 the front, and thus a sharp-cutting edge is preserved. 



The RoDENTi.A. are widely spread over the globe, and comprise 

 nearly one-half of the mammalia. From the equator to the coldest 

 latitudes they tenant rocks and mountains, plains and woods, and often 

 devastate the cultivated domains of man. 



RATS AND MICE. 



The family MURID.-E contains no less than tliii-ty-scvcn genera, and 

 three hundred and thirty species. The characteristics of the family may 

 be summed up as follows : a pointed muzzle, a cleft upper-lip, round, 

 deep-black eyes, and a long, naked tail covered with square scales, and 

 bearing only a few stiff hairs. The fore-feet have four toes, the hinder 

 ones five toes. The family is divided in common parlance into Rats 

 and Mice. The former are stout and repulsive in appearance, the latter 

 slender and graceful. The former are recent immigrants into Europe, 

 the latter have, from the earliest periods, haunted the house. 



GENUS MUS. 



This genus is divided by some naturalists into one hundred, by others 

 into one hundred ^.ud twenty species. We can find space to mention only 

 the most marked, or the best known forms. Not a single indigenous 

 species of the genus is found in either North or South America. 



The Black Rat, Mus rattus (Plate LI 1 1), is the Rat of fable. It 

 was the Black Rat which, according to tradition, devoured the wicked 

 Bishop Hatto, in his tower in the Rhine, which is still called the Mouse- 

 tower, and which wrought such havoc in ffamclin till the charm of the 

 Pied-piper freed the city. 



In all probability the Black Rat came from Persia, where they still 

 abound. In Europe, however, since the beginning of the last century, 

 it has been nearly exterminated by the Brown Rat. 



The Brown Rat, Mus deeumanus (Plate LI 1 1), is larger than the 

 Black Rat, and is of a brownish-gray color. It seems to have come from 

 Central Asia. Pallas, in 1727, describes it as migrating from the vicinity 

 of the Caspian, in consequence of an earthquake. It crossed the Volga 

 in swarms, and proceeded steadily westwaixl. In 1732 the same rat was 

 brought by ship from the East Indies to England. It appeared in East 



