WORMS 165 



and otocysts. The latter are sacs containing crystals of carbo- 

 nate of lime, and their function is supposed to be that of hearing. 

 The flatworms are hermaphroditic, and their propagation is by 

 means of eggs. They are numerous and very generally distrib- 

 uted, occurring in fresh and salt water, on land and shore, on 

 the surface and in the depths of the sea. A vast number also are 

 parasites and infest, internally or externally, nearly every living 

 creature. The parasitic forms differ anatomically from the free- 

 living worms. The internal parasites, living by absorption of the 

 digested food of their hosts, have no digestive organs ; they are 

 also devoid of organs of sense and of defense. The external 

 parasites, being carried about by their hosts, are without organs 

 of locomotion. 



CLASS TURBELLARIA 



The turbellarians are the simplest group of bilateral animals 

 and occupy the lowest place among worms. They owe their 

 name to the fact that they are covered with cilia, which are con- 

 stantly in motion and cause a slight turbulence in the water 

 around them. 



ORDER POLYCLADIDA 



C" Many-branched") 



The polyclads are found below half -tide mark on the under side 

 of stones and on seaweeds. Sometimes they are found swimming 

 about at night. They are leaf -like in form, one inch to two inches 

 in length, and are very thin and delicate. They adapt themselves 

 to the inequalities of the surfaces to which they attach them- 

 selves, and often are of the same color, and therefore are so incon- 

 spicuous that they are apt to escape notice. They move with a 

 gliding motion over surfaces, and often swim when in search of 

 food. 



The intestine is much branched and has no anal aperture. 

 From the mouth, which is placed in the center of the ventral sur- 

 face, a pharynx, or muscular fold, is protruded in some species, 

 which enables the worm to attach itself to and consume prey of 

 considerable size. After digestion has taken place, the fees'. 



