233] TURBELLARJA FROM THE MISSISSIPPI BASIN— HIGLEY 39 



out sharply against the circle of the phar3mx. The intestine is broad, its 

 diameter being very little less than that of the body; the wall is well marked 

 and soHd. It is not an even cylinder but shows a tendency to widen at each 

 fission plane. This brief surmnary emphasizes the many minor variations 

 which may be evolved in different environments. 



Macrostoma sensitivum Silliman 1884 



One individual of this species was taken from a small pond in which seven 

 other rhabdocoels occurred in larger or smaller numbers. In most respects it 

 agreed very closely with Silliman's description but in regard to a few points, 

 added details may be of value. The rhabdites which are arranged in groups 

 of two or several, he in large, spherical cells. In shape, these rods are long 

 and straight, rounded at one end and somewhat pointed at the other. Gen- 

 erally, tho not always, they lie parallel to each other. The rhabdite-bearing 

 cells are scattered evenly over the surface of the body and not at all gathered 

 into tracts. In the cytoplasm there are a number of large, light colored glob- 

 ules, placed in close proximity to the rhabdites. These globules are relatively 

 large and prominent and evidently have to do with the functioning of the cell, 

 tho whether they are stored nutriment or are merely a by-product of the heavy 

 metabolism is not clear. 



The sensory organs are also noticeable. The eyes are very far apart, nearer 

 the lateral margin than the middle line of the head. The sensory hairs are 

 clear, sharply pointed and seem often to be bent back at right angles to about 

 the middle. This bending may be directly opposite to the position of the 

 cilia, a fact which seems almost impossible. In general these hairs are evenly 

 distributed, but sometimes they may be grouped in tufts of six or eight. 



The digestive system as a whole varies not at all from the eastern t3^e 

 but the muscular power of the pharynx seems extraordinarily developed. The 

 mouth with its boundary of heavy glandular cells may be protruded as a cone- 

 shaped elevation which is constantly being turned from side to side. The 

 muscular development extends back thru one-fifth the length of the intestine 

 and is very conspicuous in the live animal. 



The reproductive organs are also noteworthy. The chitinous portion of 



the copulatory apparatus is bent, as usual, but the whole tip is broader and 



heavier than in the original diagrams. The eggs develop, a number at a time 



and crowd forward, stretching the oviduct and filHng the space between the 



intestine and the body-wall. This brief summary covers the main details of 



variation. 



Macro stoma album no v. spec. 

 Figure 21 



Of the three genera which make up the family Macrostomidae, only one is 

 represented in the eastern states. Two species, Macrostoma appetidicvJatum 

 O. Fabricus and Macrostoma sensitivum Silliman have been found, as a few 

 specimens at two or three different times in this study. The former has also 

 been taken at Lincoln, Nebraska, and thus the distribution appears wide-spread. 



