Survey of the Animal Kingdom 297 



mission. The esophagus is without a bulb; the mouth has a pair of lateral lips or 

 may be lipless. They are the cause of many diseases. 



Examples: Human filarial elephantiasis worms, Wuchereria (Filaria) bart- 

 er of ti (Fig. 101), which causes human elephantiasis by obstructing the flow of 

 lymph, especially through the lymph glands (is transmitted by nocturnal mos- 

 quitoes), guinea worm or "fiery serpent" (Dracunculus medinensis) which is an 

 inhabitant of the skin of human beings, dogs, etc., and the "eye" worm (Loa loa) 

 which affects the human eye. 



Order 4 — Trichinelloidea (trik i nel -oid' e a) (Gr. trich. hairlike). — 

 All are parasitic. The body is divided into a more or less distinct esophageal region 

 and a posterior region; the esophagus is a nonmuscular tube of cuticle embedded 

 in a single layer of epithelial cells. Females have a single ovary with a duct; 

 males have one spicule or may have none. 



-Mouth- -rt 



Female 



Anas 



VJjBS. 



Male 



Anus 



A 



B 



Fig. 101. — Wuchereria {Filaria) bancrofti of the class Nematoda, phylum 

 Nemathelminthes. A, Causes of human elephantiasis; B, a chronic enlargement 

 and hardening of the skin, particularly of the legs. Note the comparative sizes of 

 the male and female. 



Examples: Human Trichina or pork roundworm (Trichinella spiralis) (Fig. 

 100) which causes human trichinosis when improperly cooked pork is eaten (the 

 saclike cysts in which the immature stages are spent may be so numerous that 

 100,000 may be present in one cubic inch of meat). The worms may be present in 

 the muscles of man, dogs, rats, pigs, rabbits, and mice. Human whipworms 

 (Trichuris trichiura) inhabit the cecum and appendix of man. 



Phylum 7. Trochelminthes (trok el -min' thez) (Gr. trochos, wheel; helmins, 

 worm) or P. Rotifera (ro -tif era) (L. rota, wheel; fero, to bear) 



General Characteristics 



Rotifers (Fig. 102) are very common, small, aquatic animals found mostly in 

 fresh water, although some are marine and a few are parasitic. They are charac- 

 terized by a bandlike disk of cilia (trochal disk) around the mouth at the anterior 



