THE LEECHES (HIRUDINEA) 



653 



17 (18) 



18 (17) 



19 (22) 



20 (2l) 



Anus at XXIII-XXIV and following somites forming a narrow 

 sucker pedicle. Gastric ceca branched once; very con- 

 tractile; no cutaneous papillae. Nearly permanent parasite 

 on fishes in Minnesota lakes. 



Placobdella pediculata Hemingway 1908. 



Anus behind XXVII; posterior segments normal. 



Placobdella (s. str.). . . 19 



Cutaneous papillae smooth and round 20 



Integuments opaque, deeply pigmented in a conspicuous pattern 



of olive green and yellow; annulus 

 a 3 without trace of a secondary 

 furrow; size large. Common on 

 Chelydra, etc. 

 Placobdella parasitica (Say) 1824. 



VIII 



One of the best known of our leeches, 

 most often found clinging in large 

 numbers to the naked skin at the base 

 of the hind legs of the snapping turtle 

 whose blood they suck. Large indi- 

 viduals measure from 3 to 4 inches 

 long in partial extension and are very 

 broad, thin, and foliaceous. When 

 bearing eggs or young they often leave 

 the host and for a time lead a free life 

 in ponds and streams, feeding on 

 worms and larvae. Eggs and young 

 are borne in large numbers and it is 

 an interesting sight to observe the 

 crowded family of youngsters actively 

 bending and turning on the venter of 

 the parent, the thin margins of whose 

 body are inrolled to form a protecting 

 fold. The color pattern is rich and 

 striking, the ground color of dull green 

 or olive green standing in sharp con- 

 trast to the bold and characteristic 

 markings of yellow by which it is re- 

 placed to a varying degree. 



FIG. 998. Placobdella parasitica. External 

 metamerism, central nervous system, re- 

 productive organs, etc. I-XXVII 

 somites; mg, ol, I, m, marginal, outer 

 lateral, lateral and median sensillae re- 

 spectively; phg. 1 " 2 , pharyngeal glands; 

 oe, esophagus; s, atrium or spermato- 

 phore sac; d, ductus ejaculatorius; vs, 

 vesicula seminalis; $ and 9 , male 

 and female pores; vdc, vas deferens; t, 

 testes; oy, ovary. X 2. (Redrawn 

 from Whitman.) 



21 (20) Integuments translucent, brightly but not deeply pigmented "with 



green, orange, and white; a 3 of complete somites with a 

 distinct secondary cross-furrow; size medium. 



Placobdella picta (Verrill) 1872. 



22 (19) Cutaneous papillae prominent and rough or pointed 23 



23 (26) No marginal papillae on caudal sucker 24 



