130 POPULAR OFFICIAL GUIDE. 
they are rigidly protected. At present the largest colonies 
known are those in the Yellowstone Park, although in Can- 
ada and the Northwest many still remain. 
The most wonderful thing about the Beaver is the manner 
in which he builds dams, to make ponds deep enough for 
his timber-floating operations, and to afford him a sub- 
marine passage to his house. Give him a valley and a 
stream of water, and he will gladly make a pond out of 
whatever raw materials are at hand. He uses the four-foot 
sticks from which he has eaten the bark for food, and with 
these, and an abundance of mud, he will raise a good strong 
dam to a height of four feet, and a width on the ground of 
ten feet or more. The mud used is dug out of the bottom 
and sides of his pond, and carried, while swimming, be- 
tween his paws, with his front feet holding it against his 
breast. The sticks used in the dam are thrust endwise into 
the mud on top of the dam, and the mud used is patted 
down with his fore feet. The tail is not used as a trowel, 
but in swimming it is the Beaver’s propeller. 
In captivity the Beaver is not wholly a satisfactory animal. 
Like some human craftsmen, he positively declines to work 
under observation, and performs nearly all his tasks at 
night. He thinks nothing of gnawing down a tree a foot 
in diameter, and cutting its limbs into pieces which he can 
handle while swimming. If he can secure enough food- 
wood of kinds of his liking, he eats little else. Besides 
building dams to create ponds in which he can take refuge 
when hard pressed, he constructs canals, and houses for 
winter use. He also digs burrows into high banks; but his 
entrances to his various homes always are under water. 
THE ECONOMIC RODENT-REPTILE COLLECTION. 
As an answer to a frequent question—‘‘Of what use are 
reptiles?’’—a new collection has been installed in the 
Reptile House. It is supplied with descriptive labels, and 
serves several purposes. In the first place there is presented 
an elaborate series of the small gnawing animals, or rodents, 
a number of the species of which are highly injurious to the 
interests of agriculturists; secondly, the exhibition contains 
a large series of those species of snakes that prey upon the 
destructive rodents,—thus presenting for observation the 
serpents of marked economic value. Finally, the entire 
series stands as a clear demonstration of the perfect logic of 
