SOCIAL BACKBONED ANIMALS 135 



The Common Prairie- Marmot (Cynomys Ludovicianus), more 

 familiarly known as the Prairie-" Dog", on account of the barking 

 sound to which it gives utterance when alarmed, is a social 

 burrowing rodent native to the dry open plains on the east of 

 the Rocky Mountain highland. Several individuals live together 

 in the same burrow, and a very large number of these homes 

 may be associated together into a "city". The excavated earth 

 is partly heaped up into a mound at the entrance to the burrow, 

 and this may almost be called a watch-tower, since it is commonly 

 occupied by a sentinel, who performs the usual duties of his office. 

 On hearing his warning bark the neighbouring individuals scuttle 

 down into their underground dwellings. The opening of each 

 burrow is somewhat funnel-shaped, some of the earth dug out 

 having been regularly arranged round it, and pressed together 

 till firm: the use probably being to prevent flooding out during 

 sudden showers. Owing to the fact that Burrowing Owls and 

 Rattlesnakes are not infrequently found in the dwellings of this 

 rodent, the conclusion has somewhat hastily been drawn that the 

 three kinds of animal constitute a kind of " happy family ", living 

 together on the best of terms. This, however, is not the case, 

 for the Owl simply takes possession of a deserted burrow, while 

 the Rattlesnake appropriates one at random, ejecting the rightful 

 owner if necessary^ and thereafter visits his neighbours, levying a 

 tax upon their offspring. The Common Prairie- Marmot is about 

 a foot in length, exclusive of the short tail, but a larger and a 

 smaller species are also indigenous to North America. The 

 former is the Mexican Prairie- Marmot (C. Mexicanus], while the 

 smaller sort is the Columbian Prairie- Marmot (C. Cohimbianus), 

 which inhabits higher ground in the western part of North 

 America. Their habits are much the same as those of the 

 common form. It appears that there is a winter-sleep in the 

 case of individuals which live pretty far north. The True 

 Marmots (species of Arctomys) are somewhat larger animals allied 

 to the preceding, and like them gregarious burrowers. They 

 have a wide range through the northern parts of North America 

 and Eurasia, living on plains except in the southern part of their 

 distributional area, where they are typical mountain-animals. It 

 is a familiar fact that they indulge in a long winter-sleep. 



The Beaver (Castor fiber] is a very large social Rodent which 

 formerly had a wide extension in Europe and North America, 



