142 ZOOLOGY. 



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

 is partly transparent, with a dark area representing the 

 stomach, from which branch out 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 caves, which may be called Dendroccslum perccecum 

 (Fig. 94). 



The foregoing forms are easily obtained by the student, 

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

 long to the order Turbellaria, which is characterized by the 

 flat, oval body, covered with cilia. The ciliary motion can 

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

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

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

 terior part of the body of Geoplana flava Moseley, a Bra- 

 zilian land -planar ian, and posteriorly they moved backward. 



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

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

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

 side of the body, the dorsal cilia apparently subserving 

 especially this function of the speedy removal of foreign 

 substances from the surface of the body " (Moseley). The 

 structure of the flat worms may be understood by referring 

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

 European marine flat-worm. The digestive canal opens by 

 a mouth situated usually behind the middle of the body, 

 which leads into a chamber containing a cylindrical or 

 funnel-shaped proboscis, capable of being suddenly thrust 

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

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

 95, 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 the 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 



