THE LEECHES OF MINNESOTA 109 



of cornua. This median organ which evaginates to form the penis is 

 in its retracted condition spherical or inverted pyriform and has thick 

 muscular and glandular coats. 



The colors during life are very showy. Above* the ground varies 

 from a light sage green to a rich olive green with obscure longitudinal 

 stripes or short lines in the median areas. The median metameric 

 spots are cadmium orange or light red and the marginal spots black. 

 The ventral surface is a rich orange sometimes plain, sometimes spot- 

 ted with black. The colors fade very quickly in alcohol. 



Habits — This species, the native American medicinal leech, ap- 

 proaches closer to the European Hirudo mcdicinalis, both in structure 

 and habits, than any other indigenous American species, and, when 

 the use of leeches for blood-letting was more general than now, was 

 largely employed by physicians. To a limited extent it is still gathered 

 in the swamps below Philadelphia and sold for this purpose. It is 

 widely distributed throughout the northern half of the United States 

 and in Canada and is an inhabitant of standing water rather than of 

 streams or rapidly flowing rivers. Great numbers often occur in small 

 ponds and lakes. Altogether it is the best known of the American 

 leeches and has been frequently written about since its discovery by 

 Say in 1824, but its exterior has not hitherto been figured although 

 Whitman has published drawings of the annulation of a closely allied 

 species. 



Macrobdella is more strictly aquatic than the species of Hcc 1110 pis 

 and probably does not leave the water voluntarily though it will live 

 for weeks buried in the mud left by the drying up of small ponds and 

 pools in dry summers. It is an active predacious creature and swims 

 actively at the surface at night or during the day if attracted by the 

 presence of food. It is well known to the American boy who fre- 

 quently comes from his plunge in the brickyard or meadow pond with 

 several of these leeches firmly attached to his skin, an experience so 

 frequent as to have gained for it the general name of blood-sucker. 



It also attacks cattle which enter its domain to drink or cool but 

 its natural food is the blood of fishes, frogs and turtles which it attacks 

 and frequently kills. Small aquatic annelids in large numbers and 

 occasionally larval insects have been found in the stomach. In the 

 spring frogs eggs are devoured in large numbers, the eggs being sucked 

 out after the gelatinous envelopes have been cut by the sharp saw- 

 like teeth of the leech. 



In coitus the leeches cohere by means of the secretion of the copu- 



