24 ILLINOIS BIOLOGICAL MONOGRAPHS [218 



These were carefully excluded from the general results. The dark pigmented 

 portion was measured for both length and width with some note as to the 

 shape. From several hundred specimens measured, the average varies between 

 113ai and 167;u in length and 8/x and31,u in width. In general, the eyes are a 

 fairly regular kidney-shape but the percentage of difference between the two 

 eyes of the individual is high. This, however, is true for all planarians. These 

 measurements were very nearly one-half those of an average Planaria maculata. 

 The pigmented mass is a Httle more solid, not inclined to be a crescent and al- 

 ways broad in proportion to the length. The position of the eye is also signi- 

 ficant. In the river type, the eyes are always very much nearer the median 

 line than in the pond form. Thus they lie almost in the edge of the middle 

 pigmented stripe of epithelium. This situation makes their relation to the 

 whole of the unpigmented region somewhat different from that of the common 

 type. That is, lateral to the eye-pigment, one finds a very large irregular 

 clear area. This is about five or six times the width of the eye itself, and is 

 striking in its transparency. In the pond type, on the other hand, the clear 

 region, altho varying to some degree and irregular in outline, fits closely to 

 the eye-pigment leaving only a wide margin of transparent integument. 



This special character seems to be constant for the individuals found in the 

 Mississippi river or its imm^ediate vicinity. Whether it is only an environ- 

 mental change due to some immediate biologic condition or Vv^hether it is 

 developmental, rem.ains to be .'^een. 



Planaria truncaia Leidy 1851 



About the first of November, one specimen which was clearly Planaria 

 truncata, was found under a stone in a little rivulet at Milwaukee, Wisconsin. 

 The stream was hardly more than a trickle bubbling down a narrow wooded 

 ravine. .About fifty yards back from the shore of Lake Michigan, just before 

 reaching the sand of the beach region, the water splashed over a number of 

 large stones. Here was a large fauna of crustacean and protozoan species 

 with a few bits of algae in the quiet pools. Among other things on the pro- 

 tected side of a well- washed pebble was the large v/hite planarian. 



It measured about 14mm. in length and was plump and well fed. The 

 species characters were very noticeable. The sharply truncate head with 

 small dark eyes set near together and far posterior, the rather long conspicuous 

 pharynx, the white or translucent appearance and the much lobed digestive 

 tract, were all details which made the identification evident. Of these points, 

 the significant structure of the intestine is perhaps the most remarkable. The 

 contained food material was a hght brown which contrasted well with the 

 surrounding white tissue. The intestinal wall, since it was very definite and 

 to some extent non-elastic, made a clear cut outhne to the digestive tract, so 

 that the fine fingerhke branches stood out by themselves. The fact that these 

 branches do not anastomose but retain their individual shape and constant 



