8o PLATYHELMINTHES CESTODA CHAP. 



cercus) acanthotrias Weinl. (see, however, Leuckart, loc. cit. p. 

 711). 



Taenia (Hymenolepis) nana v. Sieb. 1 is found in man in 

 Egypt, Italy, England. Servia, Argentine Eepublic, and the 

 United States. Though small (^-1 inch long), its numbers 

 usually excite digestive and nervous disorders of considerable 

 severity, more serious, indeed, than those caused by the commoner 

 tape-worms. H. diminuta Hud. (flavopunctata Weinl.), normally 

 found in Eodents, has been rarely recorded in man. Taenia 

 (Dipylidiuin) caninum L. ( = T. cucumerina Bloch = T. elliptica 

 Batsch), the commonest parasite of pet cats and dogs, and T. 

 (Davainea) madagascariensis Davaine, have occasionally been 

 recorded from infants and young children. But the attacks of 

 these species are insignificant in comparison with those of the 

 cystic stage {Echinococcus polymorphus) of a tape- worm (T. echino- 

 coccus v. Sieb.) which lives when mature in the dog. 



Echinococcus is most frequent in Iceland, where it affects 2 

 to 3 per cent of the population, and a still larger proportion of 

 sheep ; while in Copenhagen, Northern Germany, some districts 

 of Switzerland, and Victoria it is not uncommon, but is frequently 

 found during post-mortem examinations when no definite symptoms 

 of its presence had been previously noticed. Echinococcus 2 varies 

 greatly in size, form, and mode of growth, but is distinguished 

 in the formation not of one scolex only, as in the Cysticercus, but 

 in the production of a number of vesicles, usually from the inner 

 wall. Within these, large numbers of scolices may be developed. 

 The whole organism continues to swell by the formation of a watery 

 liquid within it, and if its growth be rapid the fluid tension may 

 cause the rupture of the enclosing connective -tissue capsule 

 formed around the parasite, at the expense of the host, and the 

 protrusion of the daughter vesicles. It is the consequent injury 

 to the surrounding organs of the host, at this critical stage, often 

 only reached after the lapse of several years, that occasions 

 serious or even fatal results. Zoologically, Taenia echinococcus 

 and T. coenurus are interesting, since they exhibit an indubit- 



1 By Grass! this form is considered identical with T. murina. The latter 

 species is known, from this author's researches, to develop in rats without migra- 

 tion into an intermediate host. Should Grassi's synonymy prove correct, the 

 presence of large numbers of this tape-worm in man would readily receive its 

 explanation. 



2 Leuckart, loc. cit. p. 752 et seq. 



