96 HABITS AND INSTINCTS OF ANIMALS. CHAP. IV. 



taceous or naked, which do not ahsolutely crawl on their 

 belly; and who are, consequently, provided with locomo- 

 tive members particularly designed for this purpose. 



(117-) All reptiles have the power of locomotion; 

 and yet some possess, and others are altogether desti- 

 tute of, feet : in this latter case, as seen in the whole 

 of the snakes, their movements are performed by an 

 undulating motion, known to every one, but which may 

 be thus defined ; it consists in bringing up the tail 

 towards the head, by bending the body into one or more 

 curves ; then resting upon the tail, and extending the 

 body ; thus moving forward, at each step, nearly the 

 whole length of the body, or one or more of the curves 

 into which it was formed.* The progress of serpents is 

 often very rapid, so much so, indeed, as to enable them 

 sometimes to overtake a man. This is, indeed, not a 

 little surprising, in an animal that is absolutely desti- 

 tute of feet : there is reason to believe, however, that 

 the broad transverse scales, which are on the belly of all 

 such serpents as move rapidly, materially assist them, 

 not merely by their smoothness, but by their edges 

 coming into contact with the surface over which the 

 animal glides, and thus aiding it in propelling the body 

 forwards. Nor is the motion of these reptiles confined 

 to the ground; for they not only climb trees in a 

 spiral direction, but absolutely swim with inconceiv- 

 able facility, although unprovided with fins, or any 

 members analogous thereto. Instances have been re- 

 corded, of the common snake having been met with, 

 more than once, in the open channel between the coast 

 of Wales and the island of Anglesea, as if they had 

 taken their departure from the former, in order to reach 

 the latter place. In India, however, there is a distinct 

 family of venomous serpents, forming our Hydropltidce, 

 whose tails are so much compressed as to resemble an 

 oar. These reptiles live only in the water ; but they 

 swim with the head just above the surface, since their 

 respiration is very different from that of eels, which, in 



* Phil, of Zool 



