CHAPTER III 
PLATHELMINTHES 
TURBELLARIA 
A 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 two 
black eyes; the hinder end is pointed. <A variety of forms is 
found, some of which are very minute and are without an intes- 
tine or have a straight, tubular intestine, while others are much 
larger and have a branched intestine. The latter include most 
of the commoner turbellarians and those for which these direc- 
tions 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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