237] TURBELLARIA FROM THE MISSISSIPPI BASIN— HIGLEY 43 



siagnalis, which had been described by M. Schultze in 1851 as a seemingly 

 aberrant form. It possesses an armed proboscis-like structure so resembling 

 the stinging apparatus of the Nemertinea that the early authors thought it 

 must be an intermediate type. In 1885 von Graff pointed out that the so-called 

 proboscis was merely the stylus of the copulatory organ situated far anterior, 

 and that there were really no special characters to relate this species to the 

 Nemertinea. Thus the integrity of the family was settled. Eight other 

 species have been added to this genus but even yet the family remains the 

 smallest of the Turbellarian group. The nine species are strikingly similar in 

 a general way, the differentiating characters, however, being well-defined. 

 Two species, Prorhynchus stagnalis and ProrJiynchiis applanatus have been 

 found in the United States, the former in New York and in brackish water at 

 Falmouth, Massachusetts, the latter in a greenhouse in Lincoln, Nebraska, 



Prorhynchus stagnalis M. Schultze 1851 



Several specimens of this species have been found in ponds at Urbana, 

 Illinois. They were taken during the latter part of April, from the protected 

 side of a mud-bottomed little lake. They came with the loose silt from a 

 depth of three feet, where the water was fairly clear and containing little or no 

 algae. 



In a large aquarium of this same pond water, their actions were watched. 

 Superficially, they resembled little white leeches, both as to general shape and 

 the manner of retracting the whole body and then stretching it out quickly, 

 the head free, the tail attached, searching in aU directions. This motion is 

 constant for lengths of time, the animal seeming almost frantic in the quick 

 nervous motions. It crawls over the glass wall of the aquarium, covering 

 quite a distance as it does not hold its course much of the time. It also creeps 

 up and down the larger stems of Chara and other water plants, but never is 

 free-swimming. All the movements are of the muscular type and are precise 

 and quick. There is only a weak ciliary action which has little to do with the 

 locomotion, since it is as heavy when the animal is quiet as when active. The 

 power of contraction is well-developed, the animal often drawing up to one- 

 fourth the extended length. The average when at rest is, however, between 

 one- half and three-fourths the greatest extension. A noticeable fact is that 

 when drawn up and quiet the width is not changed, the extra enlargement 

 having its effect entirely upon the depth. When thus contracted, the head is 

 not generally drawn nearly straight back up to the heavier part, but is more 

 or less bent to one side so that the form is not compact but irregular. 



The general appearance is striking and characteristic. In size, there is 

 Httle variation, the length being very nearly 4 mm. and the width 5 mm. in any 

 part of the body. The shape is noteworthy, being a regular oblong with only 

 little change at any point and as a whole it is thin and flat, the only appreci- 

 able thickness being thru the intestinal region just posterior to the middle where 

 the dorsal surface rounds up a little. At both anterior and posterior ends the 



