22 ILLINOIS BIOLOGICAL MONOGRAPHS [216 



MORPHOLOGY 



FAMILY PLANARUDAE 



In number of species the Planariidae are more fully represented in the in- 

 land states than any other family of the Turbellaria. Seven species have been 

 identified, five of which are new. Planaria maculata Leidy (1848) is the most 

 common of these, occurring in abundance in nearly all rocky streams and in 

 many quiet ponds. Others appear more rarely but over such widely separated 

 areas as to suggest that they exist in much greater frequency, and in larger 

 numbers than is generally supposed. One of the species with such a widespread 

 habitat is that mentioned next. 



Planaria velata Stringer 1909 

 This worm has been taken from two very different localities, one a tempor- 

 ary puddle at Urbana, Illinois, the other a spring at Homer, Minnesota. At 

 the former place the water was black and muddy with only a minimum amount 

 of algal growth; the specimens came from the bottom mud, with the loose 

 silt, leaves, and sticks dragged up in a dip net. The conditions in the other 

 instance were almost the opposite. The planaria came from a warm water 

 spring flowing into the Mississippi and forming a little cove where almost 

 summer conditions prevailed even during the coldest weather. All the col- 

 lections both at Homer and at Urbana were made in February and March. 

 Then a large number of species flourished. The plant forms and protozoa 

 were especially luxuriant so that an ample supply of food was furnished for 

 a well populated community of microscopic forms. The list contained several 

 rhabdocoels v/hich were present in great abundance, and at least two planar- 

 ians. One of these, Planaria velata, was conspicuous among the other forms 

 by its dark brown color and lines of fragmentation to be explained later. 

 There was some characteristic variation but most of the specimens were 

 dark. Those few which did show a light gray were the small regenerating 

 individuals. The color is due, as Miss Stringer says, to a yellowish-brown pig- 

 ment which causes the general dark tinge, but which under a lens is surprisingly 

 pale and clear against the almost transparent groundwork. This pigment is 

 arranged in very small spots, either round or irregular in shape, and lying 

 in rows. These rows are paraUel, placed very evenly, close together and are 

 waving instead of straight. In general, they run longitudinally, but every 

 projection of any part, every indentation, every wound, causes a fusion or else 

 a break of the rows around it. Moreover, thruout the mid-dorsal region 

 both rows and spots are smaller and denser, which explains the heavier color 

 of the upper side. The pigment spots within the rows vary in their relation 

 to each other. They may be large and close together or far apart; they may 

 be evenly separated or not; or they may be small, scattered, or coUected in 



