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 Dcndroccelum percmcum 

 (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 TurbeUaria, which is characterized by the 

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

 be detected, as Moseley has clone, 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, 

 ^s 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. 

 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 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 



