PHYLUM VERMES 



SUBPHYLUM PLATYHELMINTHES 



Class : Turbellaria 

 A PLANARIAN WORM 



Planarian worms are very common animals in fresh-water 

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

 under-side of stones or on aquatic vegetation. They are fiat, elon- 

 gated, very soft, and contractile animals, brownish or yellowish 

 in color, and usually half an inch or less in length ; at the forward, 

 broader end is a pair of lateral sensory lobes called the auricles, 

 and on the dorsal surface are two black eyes; the hinder end 

 is pointed. A variety of forms is found, some of which are very 

 minute and are without an intestine or have a straight, tubular 

 intestine, whereas others are much larger and have a branched 

 intestine. The latter include most of the commoner turbella- 

 rians and those for which these directions have been prepared. 



Study the live animal under a hand lens. Note the gliding 

 motion with which it moves. This is accomplished partly by the 

 action of the cilia which cover its surface and partly by muscular 

 contraction. Near the middle of the ventral surface are the 

 mouth and the protrusile proboscis. Mount the animal on a slide 

 in water beneath a cover glass and observe the action of the cilia 

 under a compound microscope. Note also the rhabdites, minute 

 rods which are thickly set in the integument. 



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

 eyes and proboscis, and indicate its anterior and posterior ends. 



Study an animal which is under the pressure of a large cover 

 glass, and make out as many of the following organs as possible, 

 using often reflected instead of direct light. 



The Digestive System. The digestive canal is usually easily 



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