302 



new joints arise behind the head until the form of the tape worm 

 is attained, as in Fig. 167, after Weinland. 



Now we shall see how the eggs are produced. The hinder 

 joints become filled with eggs and then break off, becoming inde- 

 pendent animals comparable with the "parent-nurses" of the Cer- 

 carias, except that they are not contained in the body of the 

 Taenia (as in the Cercaria), but are set free. The independent 

 joint (Fig. 167, g, is called a "proglottis." It escapes from the 

 alimentary tract, and the eggs set free are swallowed by that un- 



clean animal, the pig, and the cycle of generations begins anew. 

 We thus have the following series of changes which may be com- 

 pared with the homologous series in the flukes : 



2. Morula. 



3. Double-walled sac (Planula?). 



4. Proscolex, free embryo with hooks, surrounded by a blasto- 

 dermic skin (Amnion?). 



5. Scolex (Cysticercus, larva). Body few-jointed. 



6. Scolex (Tamia). Body many-jointed. 



7. Proglottis (adult). 



Egg. 



