142 ZOOLOGY. 



submerged stones, sticks, and leaves in ponds. The body 

 is partly transparent, with a dark area representing the 

 stomach, from which branch ont at right angles a multi- 

 tude of coecal canals (gastric coeca). It has two small 

 black eye-specks. Closely allied to this flat worm is an eye- 

 less form inhabiting the streams of the Mammoth and ad- 

 joining cares, which may be called Dendroccelum jaercacum 

 (Fig. 94). 



The foregoing forms are easily obtained by the student, 

 Trho can study their habits in confinement. They all be- 

 long to the order TurieJlaria, wliich is characterized by the 

 fiat, oTal body, covered with cilia. The ciliarj" motion can 

 lie detected, as Moseley has done, by placing a little arrow- 

 root meal or fine bits of paper on the buck of the animal ; 

 these were seen to move in a forward direction on the an- 

 terior part of the body of Geoplana fio.va Moseley, a Bra- 

 zilian land-planarian, and posteriorly they moved backward. 



" In all regions of the dorsal surface it moved outward, 

 as was observed by Fritz Muller, at the same time as back- 

 Trard or forward, and was thus rapidly thrown off at the 

 side of the body, the dorsal cilia apparently sttljserTing 

 especially this function of the speedy removal of foreign 

 substances from the surface of the body " ^iloseley). The 

 structure of the flat worms may be understood by referring 

 to Fig. 95, which illustrates the anatomy of a common 

 ZEuropean marine flat-worm. The digestive canal opens bv 

 a mouth situated usually behind the middle of the bodv, 

 which leads into a chamber containing a cylindrical or 

 iunnel-shaped proboscis, capable of being suddenly thrust 

 out. The digestive canal is either a short bUnd sac, or is 

 long, forked, and either simple or much branched (Fiar. 

 S5, e). 



These worms have a so-called water-vascular system, con- 

 sisting of two lateral canals and numerous branching lat- 

 eral stems, with a common opening or pore in tlie skin be- 

 tween the two main stems, or there may be many pores. 

 The vessels are ciliated within, and are supposed to have a 

 respiratory or excretory function. The nervous system con- 

 sists of a double ganglion situated on the front end of the 



