PHYLUM PLATYHELMTNTHES 



281 



find their way usually to the veins of the bladder or the large intes- 

 tine and thence to the sub-mucous tissue, where they become 

 sexually mature. 



The commonest human Cestode parasites among Europeans are 

 Taenia solium and T. saginata (otherwise called T. mediocanellata). 

 The cysticercus stage of T. solium (Cysticercus cellulosce) occurs, 

 as already stated, chiefly in the muscles of the Pig, that of 

 T. saginata in the muscles of the Ox ; and the relative prevalence 

 in different countries of these two Tape- Worms varies with the 

 habits of the people with regard to flesh-eating : where more 

 swine's flesh is eaten in an imperfectly 

 cooked state T&nia solium is the more 

 prevalent ; where more beef, T. saginata. 

 Bothriocephalus latus, a very large tape- 

 worm without hooks, and with a pair of 

 longitudinal sucking-grooves on the head 

 instead of ordinary suckers, is a common 

 human parasite in Eastern countries. Its 

 cysticercus, which is elongated and solid, 

 occurs in the Pike and certain other fresh- 

 water Fishes. 



Of all the Cestode parasites of man, how- 

 ever, the most formidable is one which 

 occurs in the human body, not in the 

 sexually mature or strobila condition, but 

 in that of the cysticercus. This is Tcenia 

 echinococcus, the presence of which produces 

 what is termed hydatid disease (p. 278). 

 The adult Tcenia echinococcus is a very 

 small tape- worm with only three or four FIG. 231. sniiarzia 



. .-r . J . tobia. The female (?)lym? 



proglottides, occurring in the intestine or in a \entrai groove of the 

 the domestic Dog. The eggs passing out " 



with a liberated proglottis in the fseces 

 may reach the alimentary canal of Man 

 uninjured in drinking water, on the surface of salad vegetables, 

 and the like ; and, the egg-shells becoming dissolved, the contained 

 hooked embryos bore their way to the liver or the lungs or some 

 other organ. Arrived at its final destination, the embryo develops 

 into a cyst, which may become of enormous size. In the interior 

 of the primary or mother-cyst are developed a number of secondary 

 or daughter-cysts, and from the walls of these, both internally and 

 externally, are formed very numerous scolices in the way already 

 described (p. 278). Hydatid cysts are very common in some 

 domestic animals (Oxen, Sheep), as well as in Man. Various other 

 Cestodes occur in the bladder-worm stage occasionally in Man- 

 e.g., the Cysticercus cellulosce of Tcenia solium. 



The most primitive of the Platyhelminthes are, without doubt, 



suckers - 



