308 EVENINGS AT THE MICROSCOPE 



conical points, as they seemed when we viewed them side- 

 wise, but flat triangular plates, with a deep notch in their 

 lower edge. Thus they partly embrace, and are partly 

 inserted in, the margin of the jaw. 



Observe now how beautifully this apparatus subserves 

 the purpose for which it is in- 

 tended. By means of its sucker, 

 the Leech creates a vacuum upon 

 a certain part of the skin, exactly 

 like that produced by a cupping- 

 glass. The skin covered is drawn 

 into the hollow so far as to render 



JAW or I.EECH (in part). ft quite tense, by the pressure of 

 the surrounding air. Thus it is brought into contact with 

 the edges of the three jaws, to which, by means of power- 

 ful muscles attached to them, a see -saw motion is com- 

 municated, which causes the little teeth soon to cut through 

 the skin and superficial vessels, from which the blood be- 

 gins to flow. The issue of the vital fluid is then promoted 

 by the pressure around, and so goes on until the enormous 

 stomach of the Leech is distended to repletion. 



It has been suggested that this whole contrivance, with 

 the instinct by which it is accompanied, is intended for 

 the benefit of Man, and not of the Leech. Blood seems 

 to be by no means the natural food of the Leech; it has 

 been ascertained to remain in the stomach for a whole 

 twelvemonth without being digested, yet remaining fluid 

 and sound during the entire period: while, ordinarily, such 

 a substance cannot in one instance out of a thousand be 

 swallowed by the animal in a state of nature. Whether 

 this be so or not whether man's relief under suffering 

 were the sole object designed, or not it was certainly one 



