UNSEGMENTED WORMS. 185 



229. Laboratory Exercises. An extended laboratory study of these 

 groups is not desirable, yet the teacher should secure enough material 

 representing the various included phyla to enable the student to justify 

 the separation of these uncertain forms from the more exactly defined 

 phyla; and to show him how ill-defined is the assemblage which we have 

 thus brought together. The Tape-worm of man may sometimes be secured 

 from physicians, and other species of Tania are found not infrequently 

 as intestinal parasites in cats, dogs, or other animals dissected in the 

 laboratory. The general form, the method of attachment to the host, the 

 progressive development of the proglottides or " segments ", and the dif- 

 ference between these segments and those of the Earth-worm should be 

 noted. Permanent whole mounts of a mature proglottis may be made, 

 showing the embryos in the uterus. Demonstrations of the structure of 

 the proglottis may be given by properly prepared transverse sections, if 

 the equipment and time allow. 



An hour's work may profitably be devoted to the study of some one 

 or more of the common Rotifers, which may be found in water taken 

 from the stagnant pools in which there is much decaying matter. They 

 are microscopic animals and are to be recognized by the possession of 

 discs at the anterior end, which present the appearance of rotating wheels 

 because of a rhythmic action of the cilia. Make sketches showing the 

 change of shape which the animal undergoes. How is the change effected? 

 How is locomotion accomplished? What evidences have you of its ability 

 to receive stimuli and to respond to them ? How does it get food ? Can 

 you trace the digestive tract in the body of the animal ? Notice the con- 

 tracting object just back of the mouth. What conclusions do you reach 

 as to its function? Give your evidences. Verify by consulting some text- 

 book. Can you prove from what you see that this is not a single-celled 

 animal like Stentor? The student should be cautioned against taking 

 these specimens as closely typical of the whole group of Rotifers, since 

 there is very great variety of form among them. 



Planarians often appear in the laboratory in water containing an 

 abundance of decomposing organic matter, taken from ponds and foul 

 streams. The most important points to be noticed are their general form, 

 the method of locomotion, sensitiveness to stimuli, and life habits. Non- 

 sexual reproduction by fission is frequent among them. 



The Polyzoa occur as tufts of many minute animals in colonies at- 

 tached to objects in the water. Plumatella is a rather common fresh- 

 water form and makes a beautiful demonstration to illustrate the ordi- 

 nary physiological processes, as motion, feeding, the action of the diges- 

 tive tract in churning the food, sensitiveness to stimulus and the like. 

 Schools near the sea-shore will find an abundance of marine material for 

 the comparison of the colonial forms of different species of Polyzoa, since 

 they are more common in salt than in fresh water. 



230. Classification and Description. Phylum Platyhelminthes (Flat- 

 worms'). In the worms of this phylum the body is flattened or com- 



