28 THE AMERICAN BEAVER. 



and vary its direction, and to assist the animal in 

 diving. It is also used to give a signal of alarm to 

 its mates. When alarmed in his pond, particularly at 

 night, he immediately dives, in doing which the pos- 

 terior part of his body is thrown out of water, and, 

 as he descends head foremost, the tail is brought down 

 upon the surface of the water with a heavy stroke, 

 and deep below it with a plunge. The violence of 

 the blow is shown by the spray which is thrown up 

 two or three feet high. While watching upon their 

 dams at night I have been startled by this tremendous 

 stroke, which, in the stillness of the hour, seemed 

 like a pistol shot. I have heard it distinctly for half 

 a mile, and think it can be heard twice or three times 

 that distance under favorable conditions. On the 

 Upper Missouri, beavers are frequently seen in the 

 river by day, or basking in the sun under its banks. 

 I have seen them dive in this river in the daytime, 

 and without giving the signal stroke. In such cases, 

 their motions, in going under, are quick and graceful, 

 the upper line of the body, from the head to the tail, 

 coming into view in a curve, although but one-third 

 of their length is above the surface at one time. 

 While swimming in a direct course, with the head 

 above the water, the tail is not used, but is extended 

 motionless behind. It is capable of a diagonal move- 

 ment from one side to the other, and vice versa, and 

 also of assuming a nearly vertical position. This en- 

 ables them to use it as a scull, which they do when 

 entirely under water, and swimming at the most 

 rapid rate. It is most flexible at the intersection 

 of the tail proper with the posterior projection of 

 the body to which it is attached. The muscles for 



