INTRODUCTION 



That the lake region of Wisconsin, Minnesota and Manitoba 

 abounds in leeches of large size and great variety has long been 

 known, and has been commented upon frequently by visitors to 

 that well-watered area. The very first recognizable descriptions 

 of North American leeches, published by Thomas Say in 1824, were 

 based upon examples observed in the territory about Lake Vermil- 

 lion in Minnesota. Since that time a number of additional species 

 have been described from localities about the western end of Lake 

 Superior. 



The richness of the leech fauna of Minnesota is fully estab- 

 lished by the splendid collections, gathered by the State Zoological 

 Survey under the direction of Professor Llenry F. Nachtrieb, which 

 form the chief basis of this report. The entire State is not repre- 

 sented in the collection, most of which came from the northern 

 section, chiefly from Lake Vermillion, Leech Lake, Mille Lacs and 

 their environs. Yet it includes twenty species — a number probably 

 greater than could be found in an area of equal size elsewhere in 

 the United States, or, so far as has been recorded, anywhere else in 

 fresh water. Leeches generally have a wide geographical distribu- 

 tion and the presence of most of these species in other parts of the 

 state is to be expected, as many of them range through the entire 

 northern tier of states or even beyond, several are circumpolar, and 

 ( ne, Glossiphonia stagnalis, is almost cosmopolitan. The occur- 

 rence of a considerable number of the species in the southern por- 

 tion of Minnesota has been ascertained through material received 

 from other sources, the most important being a collection sent to 

 me by Prof. Henry L. Osborn, which, indeed, adds one species, 

 Placobdella hollensis, not represented in the Survey collections. 



The plan of this report is to give descriptions, which are some- 

 thing of a compromise between the technical and popular, of the 

 salient features of the entire organization of each species, omitting 

 altogether those minutiae which require more than a simple micro- 

 scope or ordinary methods of dissection for their verification. 

 Fuller descriptions of many of the species will be found in a paper 

 by Castle, Some North American Fresh-water Rhynchobdellidae, 



