146 SJVAKES. 



when skimming over smooth or unresisting surfaces, this 

 swimming motion is ever easy and graceful. In the chapter 

 on Tails, we shall see what an important agent in progression 

 is this limb, whether by pressure, as in the burrowing 

 snakes, or by its oar-like or paddle -like use in rapid 

 motion. 



To recapitulate the above in a few words — first, respira- 

 tion warms the blood ; snakes are cold-blooded because 

 only a portion of the blood passes through the lungs to 

 become oxygenated, and in proportion to the diminution 

 of the quantity of blood transmitted to the lungs, so does 

 respiration become weaker ; therefore reptiles are less de- 

 pendent on breathing. 



Regarding the ' voice; ' of serpents, so surprising are the 

 qualities attributed to it, that one would imagine the exist- 

 ence of varieties of snakes of widely differing organizations. 

 If we were to believe all we read of the sounds they produce. 

 'Hissing loudly,' or 'whistling,' Is the rule. No ordinary 

 writer or traveller who says a word about a snake ever 

 heard it hiss anything but 'loudly,' a statement traceable 

 to the same sentiment which causes persons to talk of the 

 Miorrid forked tongue.' A benevolently -disposed snake 

 who would warn you away with that terrible tongue would 

 also strengthen his argument by a prolonged hiss, and the 

 louder the better. 



But let us turn to the hard, cold, unpoetical, unimagin- 

 ative language of science, and see what a snake can really 

 do in the vocal expression of its feelings. 



Says Dr. Carpenter: 'In all air-breathing vertebrata the 

 production of sound depends upon the passage of air through 



