THE LEECHES (HIRUDINEA) 649 



parasite on the sheepshead of the lakes of Minnesota, its sucker 

 becoming fixed into deep pits in the inflamed tissues of the isthmus. 

 Many of this family are temporary parasites on turtles, frogs, 

 salamanders, etc., but also live free and subsist upon aquatic 

 worms, mollusks, etc. Because of the nature of their food the 

 smaller species are known as snail leeches. The Herpobdellidae are 

 voracious destroyers of aquatic worms, larvae, insects, and even of 

 their own kind. Many of the Hirudinidae have similar habits but 

 also burrow into mud. Some even habitually leave the water in 

 quest of earthworms and one, Haemopis lateralis terrestris, inhabits 

 garden soil several miles from water. 



While most species will partake of vertebrate blood, especially 

 just before the breeding season, Macrobdella is our only native true 

 sanguivorous jawed leech. While young it feeds upon larvae and 

 worms and attacks vertebrates only when mature, and even then 

 varies the blood diet with an occasional meal of frogs' eggs. This 

 and other jawed leeches painlessly make a trifid incision in the 

 skin and quickly extract more than their own weight of blood, the 

 flow of which is facilitated by a ferment which prevents coagula- 

 tion. As the blood fills the gastric ceca its fluid constituents are 

 drawn off through the walls and exude in droplets from the neph- 

 ropores. The solid parts remain and, protected from decay by a 

 preservative secretion, may not be completely digested for upwards 

 of a year. 



The short, flat triannulate Glossiphonidae are poor swimmers 

 but sometimes active creepers. When disturbed they roll into a 

 ball, pill-bug-like, and fall to the bottom, soon to creep hastily to 

 shelter. Species with longer, more complex segments are better 

 swimmers and the elongated and muscular Herpobdellidae and 

 Hirudinidae swim powerfully, moving rapidly with graceful undu- 

 lations in either the vertical or horizontal plane. Their resting 

 attitudes are varied and characteristic. Probably in order to facili- 

 tate respiration many species attach one or both suckers and wave 

 the body with an undulatory motion. Most leeches are nocturnal 

 and except when stimulated by hunger and the proximity of food 

 they avoid the light by hiding beneath stones, among plants or in 

 the mud. 



