656 FRESH-WATER BIOLOGY 



36 (i) Mouth large, occupying entire cavity of sucker; pharynx not 



forming a proboscis; jaws often present. 



Suborder Gnathobdellae . . 37 



37 (54) Eyes typically five pairs on somites II- VI, arranged in a regular sub- 

 marginal arch; complete somites five-ringed; toothed jaws 

 usually present; genital ducts complex, usually with a pro- 

 trusible penis and muscular sheath (atrium) and a vagina 

 of corresponding length; testes strictly paired, usually nine or 

 ten pairs; stomach with at least one pair of spacious ccca; 

 size generally large Family Hirudinidae . . 38 



38 (43) Jaws prominent, teeth numerous, in one series; ceca along entire 

 length of stomach. True blood-suckers 39 



39 (42) Copulatory gland pores on somites XIII and XIV; penis conical; 



dorsum with metameric median red and lateral black spots. 



M acrobdella \'Gr rill 18^2 . . 40 



40 (41) Genital orifices separated by five annuli. 



Macrobdella decora (Say) 1824. 



The species of Macrobdella are the nearest approach in our 

 fauna to the medicinal leech of Europe but at times vary the 

 diet of blood with frogs' eggs and worms. M. decora is well- 

 known as a voracious infester of swimming holes and of drinking 

 places for cattle and has received the name of "blood-sucker." 

 After coitus, during which the copulatory glands function, 

 spongy cocoons are formed and deposited to hatch in the mud 

 by the side of ponds and streams. Widely distributed; reported 

 from ]\Iaine to Minnesota and from Pennsylvania to Kansas, 

 northward into Canada. Frequently used by physicians instead 

 of imported leeches for blood-letting. Said to be equally eflBca- 

 cious of the smaller capacity, about 5 gm. It is so powerful that 

 serious results have followed its attacks on legs of children wading 

 in ite haunts. 



Fig. 1003. Macrobdella decora. Reproductive organs (in part) dissected. 

 at, atrium; cgl, copulatorj' gLnds; de, ductus ejaculatorius; ep, epidi- 

 dymis; gXI-XIV, ganglia XI to XIV; os, ovisac; od and ode, oviduct; 

 ov, ovary; ij and ^, first and second pairs of testes; vd, vas deferens. 

 X 3. (After Moore.) 



41 (4c) 



Genital orifices separated by two and one-half annuli. 



Macrobdella sestertia Whitman 1886. 



