SOME AQUATIC WORMS, ETC. 



193 



Although the observer may not be able distinctly to 

 see these scales, the very long, characteristic caudal 

 branches, with their joints, and the sulcation behind 

 the mouth, will be sufficient to identify the specimen. 



IV. TURBELLARIA. 



The ciliated or Turbelldrian worms seem to prefer 

 the bottom of shallow ponds, probably because the 

 food supply there is better and more easily obtained. 

 They are soft and flexible, and some are slightly 

 changeable in shape, having the power to lengthen 

 themselves, to extend the posterior border into a short 

 projection, or to narrow the front into an apology for 

 a head. Some, however, have the anterior region 

 naturally prolonged into a short snout. They are 

 usually brownish and almost opaque, the opacity being 

 increased by the large amount of food commonly pres- 

 ent in the stomach. Three forms are shown in Fig. 



145- 



Fig, 145. — Three Turbellarian wurras. 



The cilia clothing the entire surface are visible only 

 under a high power. The result of their motion, how- 



14 



