HABITS OF CRYPTOBRANCHUS ALLEGHENIENSIS. 9 



value to it principally as a means of concealment while lying in 

 wait for prey. The head, especially, resembles a flat stone 

 covered with silt ; when the animal is lying in a favorite position, 

 under a rock with only the head exposed, it is extremely diffi- 

 cult to recognize it. 



Locomotion. — The ordinary method of locomotion is by crawl- 

 ing slowly along the bottom. The limbs extend laterally and 

 give little support, so that the abdomen lies in contact with the 

 bottom. The order of movement of the limbs is the same as 

 that of a trotting horse ; the limbs which move together in the 

 same direction are associated in diagonal pairs (Marey, '79). 

 The pressure of the body on the ground is always diagonal ; the 

 body is supported and moved forward by a right fore foot and a 

 left hind foot at the same time the other two limbs swing free 

 from the ground and reach forward. The result is that the limbs 

 on one side of the body are brought nearest together while those 

 on the other side are extended furthest apart. The movement 

 may be illustrated by two persons paddling a canoe, each with a 

 long double-bladed paddle grasped by the middle ; let one 

 execute a stroke on the left hand at the same time the other 

 makes the same movement on the right ; let this performance be 

 alternated with a similar one in which each person makes a stroke 

 on the side opposite from that previously taken by him. 



Cryptobranchus is also a good swimmer. In swimming the 

 body undulates in a horizontal plane, like that of an eel, and the 

 tail shares in this motion ; in the most rapid swimming the motion 

 of the tail is very vigorous, and is the principal means of propul- 

 sion. The legs, however, are of considerable use in swimming, 

 both to propel and to guide the body and to preserve its equi- 

 librium ; during swimming at a moderate rate of speed the legs 

 are the main propelling organs. The legs preserve their usual 

 order of movement during swimming. Swimming is, then, 

 effected by the combined motion of body, limbs and tail, the limbs 

 playing a more important part in propulsion than the lateral fins 

 of most fishes. Hence the swimming movements, as compared 

 with those of fishes, present an advance toward those of most of 

 the higher animals, which swim by the use of the limbs. Crypto- 

 branchus often swims close to the bottom, so that locomotion is 

 effected by a combination of crawling and swimming movements. 



