Leeches 17 



The American medical leech, M. decora, though smaller than 

 H. grandis, seldom exceeding six to eight inches in full extension 

 and much less bulky, is nevertheless far more powerful and active. 

 In spite of the belief of some of the camp directors to the contrary, 

 all of my investigations showed that this is the only species that need 

 be considered in connection with the attacks on bathers, though both 

 H. marmoratis and E. punctata will attach themselves to bleeding 

 cuts. 



The following description shows that M. decora is a very clearly 

 characterized species distinguished at a glance from any other 

 American leech except the nearly related M. sestertia Whitman, 

 which is a little known species not reported from this State. 



THE NATURAL HISTORY OF MACROBDELLA DECORA (SAY) 



VERRILL 



Description. The American medicinal leech may reach a length 

 of ten or even twelve inches and a width of three-quarters to one 

 inch, but such huge examples are rarely found, the usual length in 

 extension being from three to six inches and the width about half an 

 inch. The body is flattened throughout and the margins are sharp, 

 much more so than in the species of Hcemopis, which in life are 

 rather rounded. During life, however, the body is very soft and 

 plastic and assumes an astonishing variety of shapes and interesting 

 attitudes. 



The anterior or oral sucker is a powerful organ provided with a 

 rather wide, unsegmented, and very mobile border, which very 

 materially increases its extent. Anteriorly, a distinct median notch 

 corresponds with a deep ventral furrow which divides the upper lip 

 and is flanked by a pair of slightly shallower furrows (figure 12, A). 

 The upper lip can be folded into the mouth cavity and almost con- 

 cealed by the lateral lobes that close beneath it. As usual in the 

 family there are five pairs of eyes, which are larger than those of the 

 species of Hcemopis, but similarly arranged in a regular submarginal 

 arch. 



When fully developed the clitellum or girdle is firm and thick and 

 extends over eighteen annuli, from the last ring of the tenth segment 

 to the second ring of the fourteenth segment inclusive, but it is 

 seldom so well-marked or so extensive. In the ordinary condition 

 the male genital pore appears as an opening of considerable size in 

 the furrow between the eleventh and twelfth segments into which the 

 surrounding rugosities converge. The inflected parts may be everted, 

 as they are during sexual activity, when they form a prominent 

 conical organ with deeply fluted sides and the small male aperture 

 at the apex. The female orifice is a small opening with furrowed 

 margins situated five rings behind the male pore. Very character- 

 istic are the copulatory glands, which may be seen already in the 

 leeches immediately after emerging from the egg, capsules or when 

 only three-quarters of an inch long. When fully developed they 

 form a conspicuous group behind the female opening, occupying a 



