THE LEECHES OF MINNESOTA 87 



from 02 on the ventral side, XXV and XXVI are wholly or partially 

 biannulate and XXVII uniannulate. 



The alimentary canal is nearly as in P. parasitica but the 

 compact salivary glands have no median lobe and the divisions of 

 the gastric creca, although long, are less numerous. The repro- 

 ductive organs are essentially similar in the two species, with the 

 sperm sac, epididymis and ductus ejaculatorius compactly folded in 

 somites XI and XII. 



Owing to the numerous papilla? and the translucency of the 

 skin the colors are a somewhat confused mixture of light and dark 

 browns, yellows and greens, based upon a fundamental pattern 

 similar to P. parasitica and consisting of a variegated brown ground 

 with light intermetameric marginal spots, a median dorsal light 

 stripe interrupted by short dark brown or brownish green longi- 

 tudinal lines, which sometimes unite into a continuous dark line, 

 and numerous small light yellow or green spots corresponding to 

 the papilla? and sensilla?. The ventral surface is plain gray or light 

 brown without longitudinal stripes. 



Habits — Placobdella rugosa, the rough leech, is a very frequent 

 inhabitant of streams and ponds, where it may be found clinging 

 to the under side of stones and floating wood, especially during the 

 late spring and early summer. At other seasons they are some- 

 times found upon aquatic turtles upon whose blood they in part 

 subsist. Leeches of this species are sluggish and when exposed in 

 their resting places press the flat body closely to the stone or log, 

 whose colors they so closely simulate, and trust to this protective 

 resemblance to escape detection, rather than creep actively away in 

 the manner of many other species of allied leeches. The close 

 resemblance to surroundings is much enhanced by the fact that 

 particles of mud adhere to the mucous and rough papilla?. Further- 

 more the leeches may partially bury themselves in the bottom sedi- 

 ments. They seldom swim and when thrown into the water roll 

 up and sink passively to the bottom, upon reaching which, they 

 creep to a place of concealment in a most deliberate fashion. 



So far as has been actually observed no other food than blood 

 is taken though it seems probable that the juices and even the solid 

 parts of small aquatic invertebrates may serve the same purpose, 

 as is certainly the case in the nearest ally of this species. 



The large chitimoid spermatophores may be observed as fre- 

 quently and easily as those of P. parasitica which they closelv re- 



