116 ENTOZOA. 



CHAPTER IX. 



CESTODA. 



Piirticular larva3 — Ccetiurus cerebralis of the sheep— Eose's discovery of a secoud kind 

 ofCcenurus — Several other forms now known — IN^nnian's observations — The Cysti- 

 cercus tenuicollis and C. fasciolaris — Bothriocephahdse — Structure and development 

 — Genera,— Diphyllobothrimn and Tricuspidaria — Tetrarhynchidaa — Structure, habits 

 and development — Genera. 



In the main, it may be said, the course of development is 

 pretty much the same in all tapeworms, and yet there are certain 

 larval forms, such as Echinococcus and Ooenurus, which instead of 

 separately developing into single tapeworms, become, as it were, 

 the immediate progeaitors of a great number of tapeworms. In 

 these cases, the product of a single ovum will embrace not only the 

 life-phases above indicated, but an almost indefinite multiphca- 

 tion of the same. In the case of Echinococcus, the zoological indi- 

 vidual will comprise several thousand tapeworms, whilst in the case 

 of Coenurus it will include, at least, several hundred. If all the 

 tapeworms thus proliferated from a common hydatid could remain 

 attached to the larval stock, then we should have an animal form 

 strictly comparable to a compound polyp ; each polyp, in this case, 

 would be a kind of secondary individual (strobila) made up of an 

 almost indefinite number of tertiary individuals (proglottides). 

 The development of Echinococcus will be described in detail here- 

 after, but some further account of its congener is here desirable. 



Gcenurus. — This title was originally given by Rudolphi to the 

 well-known hydatid so common in the brain of the sheep, and 

 which produces in that animal the disease termed the " staggers." 



