THE MOUSE TRIBE. 131 
litter is produced early in the spring, a second one follows during the summer. 
When their holes are rendered inaccessible by frost, water-voles are found to take 
shelter on shore, sometimes frequenting the cover afforded by an osier-bed, and on 
other occasions taking refuge in pollard willows. In spite of its feet not being 
webbed, the water-vole is an expert swimmer and diver; and its coat is of such a 
nature as to throw off the water as readily as does the plumage of a duck. Fossil 
remains of the water-vole are found in the cavern-deposits of England, and 
also in the “ forest-bed” of the Norfolk coast ; while those of extinct species of the 
genus to which it belongs, occur in the Pliocene crag-deposits of Suffolk and Essex. 
Short-Tailed In addition to the water-vole, the British Islands (exclusive of 
Field-Voles. Jyeland) possess two other species of the same genus, the commonest 
of which is the short-tailed field-vole, or field-mouse (J/. agrestis). This species is 

THE CONTINENTAL FIELD-VOLE (% nat. size). 
about the size of an ordinary mouse, and is greyish brown in colour above, and 
greyish white beneath, with dusky feet; the tail being about one-third the length 
of the body, while the under surfaces of the hind-feet have six naked pads. It is 
specially characterised by the circumstance that the second molar tooth in the 
upper jaw has five prisms. This character, unimportant as it may seem, serves to 
distinguish this species from the continental field-vole (JI. arvalis)—represented in 
the accompanying illustration—in which, in common with the other continental 
short-tailed members of the genus, the corresponding tooth has but four 
such prisms. 
The common short-tailed field-vole is found all over England and Scotland, as 
well as the greater part of the Continent; its range extending from the north of 
Italy to Finland, and from Spain and France to Russia; but in the southern 
portion of its habitat it is less numerous than the continental field-vole. The 
English species is commonly found in meadows—especially those where the ground 
is moist, and makes extensive runs beneath the grass, in which it roams both by 
