217] TURBELLARIA FROM THE MISSISSIPPI BASIN— HIGLEY 23 



groups. Under all conditions, however, there is a fine line of connection 

 from one spot to the next. This is sometimes hardly more than a suggestion 

 of pigment, yet in some places the connecting thread is beaded and heavy. 

 These color masses are all situated in the deeper portions of the epithelial 

 cells. 



The smooth color was often interrupted by light gray Hnes running in dif- 

 ferent directions across the body. In some specimens these could be seen as 

 grooves or furrows running into more or less conspicuous notches at the edge 

 of the body. It is along these lines that later the splitting into fragments 

 occurs. Often more than one or two lines could be distinguished at once and 

 very probably in some specimens there might have been several, since Miss 

 Stringer reports as many as thirteen fragments from a single individual. 



That the lines of fission appear so early in the pigment and skin is 

 noteworthy, since in some species the internal divisions are laid down before 

 the external are very prominent. 



Planaria maculate Leidy 1847 

 Figures 43 and 44 



In the collections which have been made in the past, Planaria maculata 

 has appeared often and in large quantities. The situations in which it lives are 

 necessarily varied, and often they are entirely opposite in many respects to 

 those where it has been found previously. Then, too, the immediate make-up 

 of a pond or stream generally changes somewhat within the length of each sea- 

 son, and much of this change is detrimental. Another point to be considered 

 is the lack of protective details, for, from many of its enemies it has no escape. 

 A summary of these conditions will explain the very apparent differences in 

 structure among the individuals of even a single pond. The variations are 

 mainly those of size,, shape, and color, and since a very large percentage have 

 suffered mutilation, there are always many specimens which show parts in 

 some stage of regeneration. Thus, structures may be altered within wide Hmits 

 and the animal still be fairly typical. For these reasons, when many planarians 

 from the Rock river showed small eyes, the fact was hardly noticed, and it was 

 not until large numbers revealed the same character that special attention was 

 given to it. Several hundred specimens were taken from different places along 

 the river, all with this same distinguishing mark. Other collections in the 

 Mississippi river, at Homer, Minnesota, at Fairport, Iowa, and also in the 

 adjoining ponds, manifested the same feature. In most respects, the characters 

 are clearly those of Planaria maculata. The variations are of the same general 

 nature, the habitat the same; the conspicuous differences are only in the size 

 of the eyes and in the surrounding pigment. Exact measurements were taken 

 of the eyes in a few specimens from every collection and approximate compari- 

 sons made for several thousand more. There were always to be found a num- 

 ber of individuals with clear white optic regions, lacking entirely any eye pig- 

 ment, and there were always individuals with eyes at some stage of regeneration. 



