THE LEECHES (HIRUDINEA) 651 



indefinitely in aquaria. For examination alive under a microscope 

 they should be stupefied and relaxed by placing a little carbon 

 dioxide (as soda water), chlorotone, or cocaine in the water. 



For preservation they should always be first relaxed with similar 

 reagents and extended before fixing. Chromic acid in one-quarter 

 to one-half per cent solutions, picro-sulphuric acid, Gilson's fluid, 

 corrosive-sublimate-acetic mixture and Fleming's fluids are all 

 good fixatives, but great care should be taken to wash out the 

 acids in order to prevent swelling of the connective tissues. Forma- 

 lin is a good preservative for general purposes. 



KEY TO NORTH AMERICAN FRESH-WATER LEECHES 



i (36) Mouth a small pore in oral sucker from which a muscular pro- 

 boscis may be protruded; no jaws. 



Suborder Rhynchobdellae . . 2 



2 (33) Body not divided into two regions; usually much depressed; eyes 

 near median line; stomach usually with well developed lateral 

 ceca Family GLOSSIPHONIDAE . . 3 



3 (28) Complete somites essentially triannulate. 



4 (13) Epididymis and ejaculatory duct forming a long, open, backward 

 loop; salivary glands diffuse; eyes simple; size small; chiefly 

 under stones and on plants in ponds and lakes. 



Glossiphonia Johnston 1 81 6 . . 5 



5 (10) Eyes one pair, well separated. Genital pores separated by one 

 annulus. 6 



6 (7) A brown chitinoid plate and underlying nuchal gland on dorsum 

 of VIII Glossiphonia stagnalis (Linnaeus) 1758. 



7 (6) No nuchal gland or plate 8 



8 (9) Greatly elongated, slender and nearly terete; without papillae; 

 very transparent; colorless; gastric ceca one pair. 



Glossiphonia nepheloidea (Graf) 1899. 



