448 
MAMMALIA. 
These animals thus make their way as far sometimes as Ger- 
many. Incalculable numbers of them perish during the journeys,, 
and scarcely a hundredth part ever live to return. 
Much discussion has taken place as to the cause which induces 
the Lemmings, as well as the Hamsters, to undertake these 
migrations. It has been sometimes asserted that they foresee a 
hard winter, and that they make these journeys to avoid it. 
But the more probable supposition is that these changes of abode 
are owing to a superabundance in their numbers, which naturally 
leads to a deficiency in the means of subsistence. 
Fig. 183. — Lemming ( Hypudoeus norvegicus). 
Musquash, or Mush- Rats — Musquash (Fig. 184) are much larger 
than Bats, their size being equal to that of a small Babbit. 
They are plentiful all over North America, especially in Canada, 
and are thoroughly adapted for an aquatic or amphibious life. 
Their hind-feet are semi-webbed, and each toe is fringed with 
straight hair; added to this, the tail, which is almost as long as 
the body, is flattened, and covered with scales. 
They possess a gland which secretes a milky fluid of a pene- 
trating musky odour ; hence the name Musk-Bats is frequently 
given them. 
These animals have a highly developed constructive genius. 
In this they resemble the Beaver, a species which we shall soon 
consider ; for they combine to build villages, in which they find a 
safe refuge against cold, and the attacks of their enemies. 
