Flatworms and Roundworms 379 



neck, so that the newest proglottids are nearest the neck. The older ones 

 at the opposite end of the worm may break from the series and be passed 

 with the feces (Figs. 182 and 183). 



Integument. — An external, very thin cuticle may give slight protection 

 to the parasite against the host. 



Motion and Locomotion. — The tapeworm is moved primarily with 

 the contents of the alimentary canal, although the hooks and suckers on 

 the scolex attach the anterior end. 



Ingestion and Digestion. — There is no alimentary tract, and the gen- 

 eral body surface absorbs digested foods from the intestine of the host. 

 There is no true coelom,. 



Circulation. — There is no circulatory system required because foods 

 are absorbed through all surfaces of the body. 



Respiration. — What little oxygen that is probably needed because of 

 its parasitic habits may be taken in through the general body surface. 



Excretion. — A pair of longitudinal excretory canals whose branches 

 end in flame cells open to the exterior, at the posterior end of the pro- 

 glottid, where wastes are eliminated. 



Coordination and Sensory Equipment. — The nervous system is simi- 

 lar to that of Planaria and the liver fluke (cerebral ganglia, lateral nerve 

 cords), although not so complex. The parasitic habits probably explain 

 the absence of sensory equipment, although suckers and hooks are present 

 for attachment. 



Reproduction. — A mature proglottid contains both male and female 

 sex organs which may be studied in Fig. 183. The eggs develop into six- 

 hooked embryos. If eaten by a pig, they bore through the wall of the 

 digestive tract and enter the skeletal muscles or other organs where they 

 encyst. Within the protective cyst, a. scolex develops from the cyst wall 

 and then everts. The larva is called a bladderworm or cysticercus (sis- 

 ti-ser'kus) (Or. kystis, bladder; kerkos, tail). If insufficiently cooked 

 pork containing cysticerci is eaten by man, the bladder part is cast off 

 and the scolex attaches to the human intestine and a series of proglottids 

 is formed by budding at the neck. 



ASCARIS 



A common roundworm, parasitic in the human intestine, is Ascaris 

 lumbricoides (as'karis lum bri -koid' ez) (Gr. askaris, intestinal worm; 

 L. lumbricus, earthworm; Gr. eidos, form). It has a long, slender, 



