PLATYELMIA; TAPE-WORMS. 317 



period of their existence in cold-blooded animals ; in these no 

 vesicle is formed, but in some there is a flat band-like appendage, 

 and in others the little vesicle of the embryo fits closely over 

 the newly formed head. 



926. Several species of Tape-worms inhabit the intestines of 

 man. Of these the best known is the Tcenia solium or common 

 Tape-worm (Fig. 635), which sometimes .measures eighteen or 

 twenty feet in length. The Bothriocephalus latus, or Broad 

 Tape-worm, is found only in particular districts on the continent, 

 especially in Holland, Poland, and Switzerland ; it is as long as 

 the common species. A third large species has been described, 

 under the name of Tcenia mediocanellata, by D. Kiichenmeister 

 of Zittau ; this appears to increase very rapidly, as, in one case 

 reported by the above author, a patient was calculated to have 

 passed on an average twenty proglottides or segments per day for 

 eighty days ; or taking the number at fifteen per day, this would 

 give 1200 proglottides; or reckoning these at 1 inch in length, 

 100 feet of worm in the above period of time, being at the rate 

 of 1 foot per day. This enormous product was all furnished 

 by a single worm. Of the Cystic forms (Scolices) a few are also 

 parasitic upon the human subject; such are the Cysticercus 

 celluloses (Fig. 636) and the Echinococcus. The former is also 

 found in various herbivorous animals, but especally in the Pig, 

 to the flesh of which it communicates the diseased appearance 

 known as measles. The Echinococci occur principally in the 

 livers of various domestic animals, but they also commonly 

 attack man in the island of Iceland. They form large bladders 

 of fluid, from the inner walls of which an immense number of 

 minute heads are developed ; and in one form or species, the 

 original bladder not only produces heads, but also smaller 

 vesicles, which again give origin to heads. The Ccenurus 

 cerebralis is another vesicular form, which attains a large size 

 and produces a great number of heads, but in this species the 

 budding takes place on the outer side of the bladder. The 

 Ccenurus inhabits the brain of sheep, to which it gives the pe- 

 culiar disease known as the vertigo or staggers. 



