III. CESTODA 



247 



Rilharzia ha-matobia is a human parasite, most common in hot climates, 

 especially among the Eellahin of Egypt. The sexes are separate. The male, 

 half an inch long, by inrolling of the ventral side (fig. 221) forms a groove in 

 which the more slender female usually lies. These united worms occur in the 

 portal vein and connected vessels, which they 

 follow and lay their eggs in the mucous mem- 

 brane of the ureters and urinary bladder, as 

 well as in liver and intestine. Several other 

 species occur in man, among them D. carnosum* 

 and D. wester nianni*. Amphistomum is com- 

 mon in the intestine of Ungulates, one species, 

 .1. Inntiinis, occurring in man. With few ex- 

 ceptions the adult Distomes occur in verte- 

 brates, the larval stages in molluscs. Aquatic 

 birds are very apt to be infested with them. 



Class III. Cestoda (Tapeworms). 



The majority of the cestodes, and 

 especially those of the human intestine, are 

 sharply distinguished from the entopara- 

 sitic trematodes. But the boundaries dis- 

 appear in forms like Archigetes, Caryophyl- 

 hcus, and Amphilina, parasitic in lower 

 vertebrates or invertebrates which are now 

 assigned to the trematodes, now to the 

 cestodes. The most important character 

 of the cestodes is that as a result of their 

 parasitic life they have lost the last traces 

 of an alimentary canal, and are nourished 

 by the juices or the partially digested food 

 of the host, since the fluid nourishment is 

 taken in through the skin. Two other 

 characters are striking: (i) The differen- 

 tiation of two developmental stages, the 

 bladder worm, or cysticercus, living chiefly 

 in solid organs (muscles, liver, brain), and 

 the sexually mature animal, living in the 

 alimentary tract; (2) the division of the 

 body of the adult into the head or scole.v, 

 and following this a series of joints or 

 proglottids. Since this last feature holds for 

 all human tapeworms, the best known species, the following description 

 begins with these typical forms. 



The sexually mature tapeworm or strobila (fig. 222) consists of a 

 scolex in front, and behind this follow in a row the proglottids. The 



FIG. 222. Tccnia saginata 

 (from Boas, after Leuckart 1 ). 

 Head with series of proglottids 

 taken from various 

 the strobila. 



regions of 



