IQ2 ZOOLOGY 



uncertain forms from the more exactly denned 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 

 worms 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 

 difference 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 contract- 

 ing object just back of the mouth. What conclusions do you reach as to its func- 

 tion? Give your evidences. Verify by consulting some textbook. 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 attached to 

 objects in the water. Plumatella is a rather common fresh-water form and makes 

 a beautiful demonstration to illustrate the ordinary physiological processes, as 

 motion, feeding, the action of the digestive tract in churning the food, sensitive- 

 ness 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. 



235. Classification and Description. Phylum IV: Platyhelminthes (Flat- 

 worms}. In the worms of this phylum the body is flattened or compressed in a 

 dorso-ventral direction, and from this fact the name is given. They are soft- 

 bodied animals without any true skeleton. There is no body cavity and no true 

 blood-vascular system. The space which would be given to such structures is 

 filled with a spongy connective tissue. Through this body-mass run the minute 

 tubes of the excretory or water-vascular system (Fig. 88, ex.}, often terminating 

 internally in special cells (flame cells, Fig. 90). These tubes have .external pores. 

 By means of this system of organs waste products, probably of a nitrogenous 

 nature, are eliminated from the tissues. The digestive tract may be wholly want- 

 ing as in the Cestodes, or a simple or forked sac, or a central sac with lateral 

 branches. It is blind, i.e., has only the oral opening. In the more complicated 

 types of stomach the much-branched sac serves the function of carrying the digested 



