306 EVENINGS AT THE MICROSCOPE 



themselves. The second pair of jaws are large, broad and 

 flat, mutually alike, and jointed on the lower side of the 

 first pair; . . . their internal edge is straight and cut into 

 deep teeth. The third pair are small, thin, concave, and 

 notched; they are affixed by their inferior edge outside 

 and in front of the second pair, which they conceal during 

 repose. Finally, the supernumerary jaw, which is found 

 on the left side only, is small, semicircular, toothed, and 

 placed between the second and third pairs. All these 

 pieces are surpassed by the margin of the proboscis, which 

 is often hard and black." l 



From this complex and formidable mouth we will pass 

 to one of quite another form, not less effective, perhaps 

 more formidable, but ordained by the goodness of God to 

 be a most valuable agent in the relief of human suffering. 

 I mean the Medicinal Leech, of which we can readily pro- 

 cure a specimen from our friend the apothecary. 



Here it is. There is no protrusile proboscis, but the 

 throat is spacious, and capable of being everted to a slight 

 degree. The front border of the mouth is enlarged so as 



to form a sort of upper lip, and 

 this combines with the wrinkled 

 muscular margin of the lower 

 and lateral portions to form the 

 sucker. With the dissecting 

 scissors I slit down the ventral 

 margin of the sucker, exposing 

 THBOAT OF LEECH LAID OPEN. fa e whole throat. Then, the 

 edges being folded back, we see implanted in the walls 

 on the dorsal region of the cavity three white eminences 



1 "Litt. de la France, " ii. 138. 



