20 GUIDE TO THE STUDY 



is absorbed directly through the integument. With rare excep- 

 tions, the life cycles of tapeworms involve at least two hosts of 

 different species. 



The class Cestoda is divided into two subclasses, the Monozoa 

 and the Merozoa. The former contains the most primitive 

 Cestoda, unsegmented forms which are of special interest as 

 showing relationships to the Trematocla, or flukes. Most of the 

 described species are from fish. 



The typical tapeworms belong to the subclass Merozoa. 

 We shall take as a type Tcenia pisiformis, one of the most common 

 tapeworms of the dog. 



PRACTICAL WORK 



Gross Examination. — -A fresh or prepared specimen of Tcenia 

 pisiformis will be furnished for examination. Note the length, 

 the shape of body, the head or scolex, the neck, and the strobila, 

 or chain of proglottides, or segments. About the middle of one 

 side of the larger proglottides note the genital pore. Do these 

 occur on the same side of all the proglottides? Count the number 

 of proglottides. Make an outline drawing illustrating these 

 points, indicating by dotted lines regions only partially 

 represented. 



Detailed Study. — Using stained and mounted preparations, 

 study carefully the following points, making enlarged drawings 

 of each region. As the specimens are thick and more or less 

 opaque, it is important carefully to regulate the lighting and to 

 use great caution to avoid injuring them. 



Scolex. — Note the shape and relative size of the scolex. It is 

 provided with four suckers for attachment to the host. In 

 addition, Tcenia pisiformis is " armed" with a double circlet 

 of attachment hooks, borne upon a slightly projecting rostellum. 

 The hooks vary in number, size, and shape in different species of 

 tapeworms and should be carefully studied in the specimens 

 available. Examine several slides giving different aspects of 

 those structures. Indicate also in your chart the short, unseg- 

 mented neck. 



Developing Proglottides. — Examine proglottides from the first 

 sixth of the body length and note the early traces of the reproduc- 

 tive organs. It should be recalled that the Cestoda are hermaph- 

 roditic. Two more deeply staining lines running in from the 

 genital pore represent the vas deferens and the vagina. In the 



