235] TURBELLARIA FROM THE MISSISSIPPI BASIN— HIGLEY 41 



are fine and are in length about the thickness of the epithelium. They are 

 distributed evenly over the surface of the body. Their movement is regular 

 and gentle with no heavy waves of motion. This lack of power is to be cor- 

 related with the crawHng rather than the swimming habit, and also with the 

 strong muscular contraction Vv'hich causes a large amount of bodily twisting 

 and turning. There is never the smooth gliding motion so characteristic of 

 types propelled by ciliary motion. The tail portion alone has specialized cilia. 

 Over the upper surface and to some extent down on the ventral side there are 

 cilia which are about four times the size of those of the rest of the body. They 

 are from twenty to thirty in number and rather irregularly placed, standing 

 out stiff and spine-like in all directions. They do not flex and wave as do the 

 others but are more rigid, thicker walled and conspicuous. They are sharply 

 pointed with somewhat broad, heavy bases, and are evidently sensory in 

 function. With this exception the integumental details appear specialized to 

 only a small degree. 



The muscular system is important. The muscles are many cells or fibers 

 running in a more or less longitudinal direction altho often somewhat oblique. 

 These connect the anterior regions with the posterior end and are the principal 

 source of locomotive power. The muscles which control the action of the head 

 are stronger on the dorsal side and run in a number of directions, interlacing 

 to form a network strong enough to lift the bulky head. The action of the 

 pharynx is also heavy and forceful; in fact this is one of the most muscular 

 species. But with all this pov/er of contraction, the muscle strands are still 

 so delicate as to be very nearly invisible. They are never concentrated as 

 to be at all solid or firm, but are rather single cells depending for their 

 strength upon the sum of all their work. 



The parenchyma is visible as a transparent material making nearly one- 

 haK the body mass. It is almost the whole of the large head and extends back 

 completely surrounding the intestine and reproductive organs, even filKng the 

 broad tail region. The cellular structure is evident even the its extreme 

 delicacy makes it appear almost a cobweb. The cells have several long, irregu- 

 lar processes, running in all directions, making a network much Uke that of other 

 forms but less heavy. 



The digestive system is thin-walled and in all specimens very nearly as 

 transparent as the parenchyma. Its boundary is somewhat irregular and the 

 elasticity or limit of extension less than in many species. The pharynx is 

 nothing more than the narrowing of the anterior end of the intestinal cavity 

 to the mouth region. It is not at all marked off from the rest of the digestive 

 tract so that its limits cannot be distinguished. The mouth when closed is a 

 thin slit just posterior to the eyes, when open it is triangular or roundish in 

 shape, the wider part being anterior. The bounding wall around the mouth is 

 heavy, about twice the thickness of the integument. It is well-defined and 

 shows the muscle strands which control it. The intestine itself extends far 

 back into the tail region but not much farther forward than the mouth. The 



