148 



THE FLATWORMS— PLATYHELMINTHES 



bathed with digested food they have found it unnecessary to have a di- 

 gestive system, and not even a vestige of this system remains. Their 

 muscular system is poorly developed and they usually just lie passively 

 in the intestine soaking up the food needed for their growth and metabo- 

 lism. When it comes to reproduction, however, we find that tremendous 

 emphasis has been placed on this system. Reproduction seems to be the 

 most important thing in a tapeworm's life judging by the development 



£U£-Hook 



Excretory canal 

 Nerve 



Testes 

 Uterus 



Vos deferens 

 Genital por 



Vagina 



Ovary 



Yolk gland 



i 



Courtesy General Biological Supply House 



Fig. 10.9. Scolex and proglottids of the common dog tapeworm, Taenia pisiformis. 

 On the left, the scolex and the immature proglottids. Note the hooks and suckers on 

 the scolex, which are used to attach the tapeworm to the intestinal wall. On the right, 

 mature proglottids. Most of the structures which are visible are organs of reproduc- 

 tion. It can be seen that each proglottid is almost a complete individual in itself. 



of these organs. A complete set of male and female organs is found in 

 each proglottid, and it has been suggested that each proglottid is a sepa- 

 rate animal that is produced by a process somewhat like budding at the 

 neck. There is good reason to think of them in this way, although they 

 do have nerve cords and excretory canals that run the entire length of the 

 worm, which tie the individual proglottids together into some sort of 

 unified whole. 



