CHAPTER III 



PLATYHELMINTHES 

 TURBELLARIA 



A TRICLAD PLANARIAN WORM 



Planarian worms are very common animals in freshwater 

 streams and ponds as well as in the sea ; they may be found on 

 the underside of stones or on aquatic vegetation. They are 

 flat, elongated, very soft and contractile animals, brownish or 

 yellowish in color, and usually half an inch or less in length : 

 at the forward, broader end, on the dorsal surface, are black 

 eye-spots; the hinder end is pointed. A variety of forms is 

 found, which may be divided into two groups, the Rhabdocoela, 

 those possessing a straight, tube-like intestine, and the Dendro- 

 coela, in which the intestine is branched. The latter include 

 most of the commoner turbellarians and those for which these 

 directions have been prepared. 



Study the live animal under a dissecting microscope. Note 

 the gliding motion with which it moves. This is accom- 

 plished partly by the action of the cilia which cover its sur- 

 face and partly by muscular contraction. In the middle of 

 the ventral surface are the mouth and the protrusile proboscis. 

 Mount the animal on a slide in water beneath a thick cover- 

 glass and observe the action of the cilia under a compound 

 microscope. 



Exercise 1. Draw an outline of the animal on a large scale, 

 with the eyes and proboscis, and indicate its anterior and 

 posterior ends. 



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