664 THE ANIMAL KINGDOM. 



vesicles sometimes grow and multiply without giving origin to scolices at 

 all. The scolex developes from a small mass of cells : see p. 230. The 

 majority of non-sexual Cestoda have the Cysticercus-form, i. e. a single 

 scolex in connection with each proscolex. The Coenurus-form, i. e. many 

 scolices in connection with a single proscolex, occurs in T. Coenurus \ and 

 perhaps in Triaenophorus . Brood-capsules which give origin to several 

 scolices are distinctive of T. Echinococcus ; or to one scolex, of an 

 Echinococcoid inhabiting the Earthworm 2 . 



The scolex ofLigula and Schistocephalus developes joints and immature 

 sexual organs while still within the first host, a Stickleback ; that of T. 

 crassicollis ( = Cysticercus fasciolaris of the Mouse) developes non-sexual 

 joints under similar conditions which however are digested when transferred 

 to the stomach of the Cat, in this instance the final host. But in other 

 Cestoda joints and sexual organs appear only when the scolex reaches its 

 last resting-place. 



Though many Cestoda are known, the life histories of relatively few 

 have been traced. The most important tapeworms inhabiting Man are 

 T. solium, the Cysticercus cellulosae of the Pig, &c. and man himself; 7! 

 mediocanellata, the Cysticercus Bovis of the Ox ; Bothriocephalus latus, the 

 non-sexual state of which inhabits the Pike and Burbot (Lota vulgaris\ 

 perhaps however only as intermediate hosts ; and T. Echinococcus^ but in 

 the non-sexual state only. The chief forms found in the Dog are given 



1 It is possible that there is more than one species of Coenurus. The identity of the two forms 

 occurring in the Sheep and Rabbit has not been established, and there are others known. 



2 Villot has proposed to classify the cystic forms of Taeniae as follows : 



I. Cystic forms properly so-called. ' The caudal vesicle originates from the Proscolex by simple 

 growth and structural modification, without the production, strictly speaking, of any new part.' 

 Cysticercus^ Coenurus, Echinococcus. 



II. Cystic forms ' in which the caudal vesicle originates from the Proscolex by budding, i. e. by 

 the addition of a new part ' = Cysticercoid forms. There is a head, the future Scolex ; a body and 

 caudal vesicle, or cystic portion ; and a blastogen = Proscolex, ' which preserves its autonomy and 

 embryonic characters.' There are two subdivisions. 



A. The caudal vesicle is formed by endogenous budding. Polycercus, the blastogen gives origin 

 to a number of individuals which are contained within it ; P. Lumbrici, the Echinococcoid form from 

 the Earthworm mentioned in the text. Monocercus, a single individual is formed and contained 

 within the blastogen ; M. Arionis ( = Cysticercus Arionis} where Villot considers what is usually 

 held to be an adventitious cyst as the blastogen ; M. G'lomeridis, from Glomeris limbatus ; and 

 perhaps some others. 



B. The caudal vesicle is formed by exogenous budding. Cercocystis, a single individual is pro- 

 duced by the blastogen and remains in connection with it; C. Tenebrionis (Stein, Z. W. Z. iv. 1853, 

 p. 205) ; Staphylocystis, the blastogen produces a colony which remain in connection ; St. bilarius <5^> 

 St. micracanthus, both from Glomeris limbatus. Urocystis, the blastogen produces a series of indi- 

 viduals which are detached ; U. prolifera from Glomeris limbatus. Cryptocystis, the blastogen forms a 

 single individual which is detached ; C. Trichodectis ( = Cysticercus T. ellipticae}, the strob ila of 

 which is T. elliptica of the Dog (Melnikow, A. N. 35, i, 1869, p. 62). See Villot, A. Sc. N. (6), 

 xv. 1883. 



Braun has proposed to divide the non-sexual forms of Cestoda into (i) Cysticerci with a vesicle 

 containing much liquid ; (2) Cysticercoidei with little fluid in the vesicle ; (3) Plerocerci, forms with a 

 small but solid Proscolex ; (4) Plerocercoidei, forms with a solid elongated Proscolex. 



