ROTIFERA. 293 



12. The embryo, in the intermediate host, becomes encysted 

 and changes directly to a scolex (plenrocercoid) or into a bladder 

 worm (cysticercus) which produces internally one or more scolices. 



13. The scolex is freed from its cyst when taken along with 

 food into the stomach of the proper host, and then acquires the 

 capacity of development into a tapeworm. 



14. In man occur as cysticerci Tcenia echinococcus (adult in 

 dog) and T. solium; as adults Tcenia solium (cysticercus in pigs), 

 T. saginata (cysticercus in cattle), and Bothrioceplialus latus 

 (pleurocercoid in fish). 



15. The NEMERTINI are distinguished by a complete alimentary 

 canal with anus, and a proboscis dorsal to the digestive tract. 



PHYLUM V. ROTIFERA (ROTATORIA). 



The aquatic wheel animalcules, or Rotatoria, are among the 

 smallest Metazoa, and can be distinguished from the Infusoria, 

 which they resemble in habits, only by the microscope. The body 

 is divisible into three regions, head, trunk, and tail. The trunk 

 is covered by a tough cuticle into which head and tail can be 



f 



FIG. 257. Diagram of rotifer. (After Delage et Herouard.) 7>, brain; /c, flame cell; 

 gy, gastric gland; i, intestine; w, mastax; ov, ovary; pg^ pedal gland; pv, pulsat- 

 ing vesicle of excretory system; g, stomach. 



retracted. The tail or < foot ' is often composed of rings which can 

 be telescoped into each other and which by their superficial resem- 

 blance to segmentation formerly led to the association of the roti- 

 fers with the Arthropoda. The last tail ring often bears a pair of 

 pincer-like stylets which together with adhesive glands enable the 

 animal to adhere to objects. The head has the most delicate 

 cuticle and is expanded in front to a trochal disc, an apparatus of 

 varying appearance, which is surrounded by a ring of cilia of use in 

 swimming and also in directing food to the ventral mouth. The 



