48 PLATYHELMINTHES. 



Class 4. Nemertinea. 



Elongated, ciliated, with eversible proboscis not 

 directly connected with the alimentary canal. 

 Intestine usually with lateral diverticula. Anus 

 present. (Tetrastemma, Cerebratulus.) 



TURBELLARIA. 



PLANARIA MACULATA. 



This form is very common in fresh-water ponds throughout 

 the United States. It is found during the day on the lower or 

 shaded surfaces of stones and other submerged objects, a fact 

 which suggests that it is nocturnal in its habits. Most fresh- 

 water planarians have very opaque bodies and their internal 

 organization cannot be studied in the fresh specimens. 



1. Notice the general shape of the body. 



2. The methods of locomotion. Look for cilia. 



3. The pharynx and mouth near the middle of the ventral 

 surface. 



4. The eye-spots on the anterior dorsal surface. 



5. Try feeding specimens by crushing a live pond-snail and 

 putting the fragments in the dish with them. If any of the 

 worms are at rest, set them in motion by lifting one end of each 

 with a bit of wood or some blunt instrument. Observe the ani- 

 mals at intervals of a few minutes and see if any of them begin 

 to feed. If so, by turning them over quickly with a blunt instru- 

 ment, try to see how the pharynx is used. If not successful, 

 try turning a specimen ventral side up, and placing a small bit 

 of snail meat on its body in the region of the pharynx. 



6. Look among the specimens in the dishes on the prepara- 

 tion table for animals that show marks of normal fission. 



7. Clean a heavy watch-glass thoroughly and pour it about 

 two-thirds full of clean pond-water from the jar on the prepa- 

 ration table. Transfer all of the specimens to this dish, lifting 

 each carefully with a bit of wood. With a scalpel mutilate 

 them in various ways; cut one transversely, another longitu- 

 dinally, another into several pieces of various shapes. Make 



