270 



EVENINGS AT THE MICEOSCOPE. 



I dissect out of the flesh, then, one of the white points, 

 say the middle one, and laying it in water in the compres- 

 sorium, flatten the drop, but use no more pressure than 

 just enough for that. Now I apply a power of 150 dia- 

 meters, and we will look at it in succession. You have 

 under your eye a somewhat pellucid mass, of an irregular 

 oval figure, and of fibrous texture, one side of which is 

 thinned away apparently to a keen edge of a somewhat 

 semicircular outline. But along this edge, and, as it were, 

 imbedded into it for about one-third of their length, are 

 set between seventy and eighty crystalline points, of highly 

 refractive substance, resembling glass. These points gra- 

 dually decrease in size towards one end of the series, and 

 at length cease, leaving a portion of the cutting edge 

 toothless. At the end where they are largest they are 

 nearly close together, but at length are separated by spaces 

 equal to their own thickness. The manner in which they 

 are inserted closely resembles, in this aspect, the insertion 

 of the teeth in the jaw of a dolphin or crocodile. 



But this appearance is deceptive. By affixing the little 

 jaw to the revolving needle, we bring the edge to face our 

 eye. It is not an edge at all ; but a narrow parallel-sided 

 margin of considerable breadth. And the teeth are not 

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

 wise, but fiat triangular 

 plates, with a deep notch in 

 their lower edge. Thus they 

 partly embrace, and are 

 partly inserted in, the mar- 

 gin of the jaw. 



Observe now how beauti- 

 fully this apparatus subserves 

 the purpose for which it is 

 intended. By means of its 

 sucker, the Leech creates a 

 vacuum upon a certain part of the skin, exactly like that 



ja-w of leech (in part). 



