261 



Anterior end pointed. Two slender sharply pointed cephalic ap- 

 pendages. Wider just in front of appendages than at any point poste- 

 rior to them except in large specimens which are of about same width 

 through pharyngeal region. Shghtly constricted just back of cephalic 

 appendages. Sides nearly parallel. Posterior end pointed. 



Color of dorsal side, to unaided eye, a uniform very dark sepia 

 brown, which gives a "velvety" effect. Ventral side slightly lighter, 

 chiefly due to thick slime layer. Under lens, a clear hght brown ground 

 with fine dark brown, almost black pigment spots, either quite uniformly 

 distributed or arranged so as to give appearance of a very close net 

 work. Non-pigmented circum--ocular spaces usually elongated in antero- 

 posterior direction and placed either just in 

 front of or in line with anterior margins of au- 

 ricles. Some with little or no pigment on po- 

 sterior margins of auricles, others with auri- 

 cles pigmented like rest of body. Small or 

 poorly fed specimens kept in aquaria someti- 

 mes with pigment more or less collected in 

 spots and lighter in color. A light median 

 streak frequently present. 



A study of the digestive tract in living 

 material is extremely difficult owing to the 

 dense pigment. The side branches from the 

 main trunks anastomose freely both in the 

 anterior and the posterior regions. From 10 

 to 40^ of sectioned specimens show one 

 cross-connection between the two main poste- 

 rior trunks a short distance from the end. 

 The percentage of cross-connections varies 

 considerably in collections from different localities. In a majority of 

 sectioned specimens and of living specimens in which it can be distin- 

 guished, the pharynx is somewhat longer than the cavity within which 

 it lies and is thus thrown into irregular transverse folds. The pharynx 

 is also rather longer in proportion to the length of the entire worm than 

 in other species with which I am familiar. 



Reproduction ordinarily seems to be by the asexual method. Al- 

 though frequent collections have been made for several years at Omaha 

 where this species is especially abundant, but three sexually mature 

 specimens have been found. These with a few specimens from the Sioux 

 County collection and from the University aquaria, are all the mature 

 material I have been able to obtain. The structure of the sexual organs 

 indicates a close relationship to P. maculata Leidy and to the South 



Fig. 4. Planaria agilis. 



Lateral view of atrial 



organs. 



