492 MAMMALIA. 



coidal placenta. In the male the testes are temporarily jjlaced 

 in the scrotum, at other times they lie in the abdomen. 



The chief families are the Murida; (Eats and jMice), the 

 ArvivoJidai (Voles), the Leporidw (Hares and Eabbits), the 

 Cavida: (Guinea-pigs), the CasforidoB (Beavers), and the Mijox- 

 idui (Dormice). All we need consider are the Mice, Rats, Yoles, 

 and Eabbits. 



MuRiDiE, OR Eats and Mice. 



In this family the tail is long as a rule, and the body is 

 long and narrowish. Hind-legs longer than the fore-legs. 

 Head pointed. The back molars possess a tuberonlate crown, 

 entirely covered with enamel. External ears clearly seen. The 

 genus Mus (Eats and Mice) have long, scaly, ringed tails. 



Three species of Eats are found in Britain — namely, the 

 Black Eat (Mus rattus), the Brown Eat (i/. decumanus), and the 

 Irish Eat (i)/. hibernicus) ; this last species, told by the diamond- 

 shape patch of white in front, is only found in Ireland and the 

 Outer Hebrides. The Black Eat only is indigenous to Euroi^o 

 (unless M. hibernicus is really a distinct indigenous species) ; it 

 is smaller than the common brown rat, which came over to 

 Europe in the eighteenth century. It was imported into 

 Britain in shipping, and is now spread all over the world. It 

 may also have entered Europe from Asia by migrating into 

 Eussia. In any case, it has increased with alarming rapidity, 

 and has quite driven out the indigenous black rat. The black 

 rat is smaller and much darker than M. decumanus, which has 

 a dusky-grey belly and a longer tail. Here and there specimens 

 are still seen, the writer having trapped it in Lundy Island. 



The Eats live upon all manner of substances, and are noxious 

 in many ways, — a great nuisance indoors, a veritable pest in 

 poultry-yards and amongst corn, whilst they also distribute 

 the trichinosis amongst pigs, a disease which rats are very 

 subject to, and still more, through their fleas, plague. 



A fourth species, Mus alexanclrinns, is sometimes found in 



