92 THE LEECHES OF MINNESOTA 



strongly ventrad. (The disc is composed of somites XXVIII to 

 XXXIV.) The few nephridopores that are visible are situated as 

 in P. parasitica. 



The mouth is very small and is situated far forward near 

 the anterior rim of the sucker in somite II. As in related species 

 the proboscis is slender, the oesophageal glands compact and the 

 stomach provided with seven pairs of large caeca reaching nearly 

 to the margins of the body. The caeca are less deeply divided and 

 simpler than those of P. parasitica, each of the first six pairs present- 

 ing only two or three rather short lobes. The intestine reaches to the 

 posterior part of somite XXIV or even beyond and then bends ab- 

 ruptly forward toward the dorsum as an extremely narrow rectum 

 to the anus situated at XXIII/XXIV. The forward curvature of the 

 rectum and the anterior position of the anus are unique features in the 

 family. 



The reproductive organs are essentially similar to those of 

 P. parasitica. The male and female external orifices are situated 

 respectively at XI/XII and XII a2/a3. Six pairs of testes are 

 crowded between the bases of the gastric caeca. The large sperm 

 sac and ejaculatory duct of the vas deferens form a compact snarl in 

 somite XII in the immediate neighborhood of the atrium. 



In addition to the type specimen taken by Professor Nachtrieb 

 from the isthmus of a sheepshead at Lake Pepin, the writer has 

 also examined specimens in the collection of the Illinois State Lab- 

 oratory of Natural History taken from the same host at Henry and 

 Peoria, Illinois. 



Habits — Hemingway gives the following account of what is 

 known concerning the interesting habits of this leech : — 



Placobdella pediculata appears to be a true fish parasite, having 

 been found only in the gill chamber of the freshwater sheepshead 

 (Aplodinotus grunniens), the posterior sucker of the leech being 

 deeply imbedded in the side of the isthmus or shoulder. In the 

 case of young leeches which have not been long attached, the de- 

 pression caused by the posterior sucker is comparatively shallow, 

 being a mere external depression in the inflamed tissues of the 

 fish. As the attachment continues the inflamed tissues of the host 

 grow up like a collar and close in around the leech's body in front of 

 the sucker. This closing in of the inflamed collar presses upon the 

 body of the leech, narrows it to a slender peduncle in front of the 

 sucker and incidentally crowds the sucker down into the tissue- of 



