. Fresh-water biology. Freshwater biology. THE LEECHES (HIRUDINEA) 653 17 (18) 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 pedicidata Hemingway 1908. 18 (17) Anus behind XXVII; posterior segments normal. Placobdella {s. sir.). . 19 19 (22) Cutaneous papillae smooth and round 20 20 (21) Integuments opaque, deeply pigmented in a conspicuous pattern "-" of ohve green and yellow; annulus a' without trace of a secondary fu
. Fresh-water biology. Freshwater biology. THE LEECHES (HIRUDINEA) 653 17 (18) 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 pedicidata Hemingway 1908. 18 (17) Anus behind XXVII; posterior segments normal. Placobdella {s. sir.). . 19 19 (22) Cutaneous papillae smooth and round 20 20 (21) Integuments opaque, deeply pigmented in a conspicuous pattern "-" of ohve green and yellow; annulus a' without trace of a secondary furrow; size large. Common on Chelydra, etc. Placobdella parasitica (Say) 1824. 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-50CVU — somites; mg, ol, I, m, marginal, outer lateral, lateral and median sensillae re- spectively; phg.^~^. pharyngeal glands; oe. esophagus: 5, atrium or spermato- phore sac; rf, ductus ejaculatorius; vs, vesicula seminalis; $ and 9, male and female pores; vdc, vas deferens; /, testes; ov, ovary. X 2. (Redrawn from Whitman.
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectfreshwa, bookyear1918
