PHYLUM PLATYHELMINTHES 



93 



up and observe quickly the white protruded pharynx which is inserted into 

 the meat. 



5. Regeneration. To save time and material members of each table may 

 work together on the following experiment: Obtain several finger bowls and 

 glass covers for them and wash both thoroughly. Take several Planaria and 

 cut them up into pieces of various shapes and sizes. Cut some very small 

 pieces. The animals are best cut by placing them on a glass plate, waiting until 

 they extend to their full length, and then making cuts with a quick, firm stroke 

 of a sharp scalpel. Place the pieces in the finger bowls with plenty of water, 

 cover with glass plates, keep out of the sun, and change the water every few days. 

 Examine at each laboratory period to observe the progress of the regeneration. 

 Make a series of simple outline drawings to show the changes in form from day 

 to day. 



Is any piece of Planaria capable of regenerating a whole worm? Are any 

 differences apparent due to differences in size or shape of the original pieces? 

 Do very small pieces regenerate as well as larger ones? 



6. General considerations on Planaria. What systems does Planaria possess 

 in common with Hydra? Are these better developed in Planaria than in 

 Hydra? What system is present in Planaria which was entirely lacking in 

 Hydra ? What systems are absent in Planaria which the frog possesses? What 

 type of tissue is present in Planaria which Hydra lacked? How do the muscle 

 systems of the two animals differ? Is the digestive tract of Planaria a gastro- 

 vascular system as in Hydra, i.e., both digestive and distributive? Does 

 Planaria still retain the protozoan method of digestion, as in Hydra (Hegner, 

 p. 155)? What is the essential difference between cross-sections of Hydra and 

 Planaria? Understand fully what are the corresponding layers in the two ani- 

 mals. To what stage in the development of the frog may the Planaria be com- 

 pared? 



B. GENERAL SURVEY OF OTHER FLATWORMS 



Examine the specimens provided and familiarize yourself with the following 

 groups of flatworms: 



1. Free-living flatworms or Turbellaria. These are slender, flat animals 

 similar in appearance to Planaria, living in water or damp places, never of large 

 size, often quite small. If living forms other than Planaria are available they 

 will be demonstrated to you. 



2. Flukes or trematodes. These flatworms are external or internal parasites 

 on other animals, particularly on vertebrates. They are broad, flattened, often 

 leaflike animals, provided with suckers and hooks for adhesion to their hosts. 

 The liver fluke, one of the largest forms, lives in the bile ducts of sheep and 

 other domestic animals. The assistant should demonstrate living flukes para- 

 sitic in the frog. The commonest are the lung fluke, Pneumoneces, found inside 





