CESTODA. 



'95 



a scolex or head, which, in another host, buds off the chain Qiprogloitides. 

 As it is virtually the same animal throughout, the life history does not 

 nclude an "alternation of generations." It is doubtful, however, what 

 term should be applied to those cases in which the bladder-worm 

 ( Ccenurus and Echinococcus] forms not one head only but many, each 

 of which is capable of becoming an adult tape-worm. The only known 

 exception to the fact that sexual tape-worms are parasites of Vertebrates 

 is Archigetes sieboldii, a simple cestode which is sexual within the small 

 fresh-water oligochcet Tubifex rivulorum. 



Representative Life Histories. 



ADULT, SEXUAL, OR TAPE-WORM 

 STAGE. 



NON-SEXUAL,PROSCOLEX, OR BLADDER- 

 WORM STAGE. 



1. Tcenia solium, in man, with four 

 suckers and many hooks. 



2. Tcenia saginata or rnediocanellata^ 

 in man, with four suckers, but JJfc hooks. 



3. Bothriocej>Jialus latus y in man, 

 with two lateral suckers, but no hooks, 

 with less distinct separation of the pro- 

 glottides than in Tania. It may be 

 ii yards in length. 



4. Tcenia (Echinococcifer) echino- 

 coccus, in dog- Very small, with three 

 joints. 



5. Tcenia ccemtrus t in dog. 



6. Tcenia serrata, in dog. 



7. Tcenia cucuwerina, in cat. 



1. Cysticercus celluloses, in muscles of 

 the pig. 



2. Bladder-worm in cattle. 



3. The ciliated, free-swimming embryo 

 becomes a parasite in the pike, trout, 

 burbot, etc., but without a distinct 

 bladder-like stage. 



4. Echinococcws veterinomm, in 

 sheep, cattle, pigs, etc., and some- 

 times in man, producing brood cap- 

 sules, which give rise to many " heads." 



5. CcenuruseerebraliS)Ca.Vis\.ng sturdie 

 or staggers in sheep, with numerous 

 "heads." Also in cattle, goat, horse, 

 etc. 



6. Cysticercus pisif or mis ) in rabbit. 



7. Cysticercus fasciolaris ) in mouse. 



Zoologically the cestodes are interesting, . on account of their life 

 histories, the degeneration associated with their parasitism, the pre- 

 valence of self-impregnation, and the complexity of the reproductive 

 organs. Practically they are of importance as parasites of man and 

 domestic animals. 



Classification. The class Cestoda includes a number of families : 

 Cestodariidse. No joints, one set of gonads. 



e.g, Archigetes, Caryophyllaus, Amphilina, Gyrocotyle. 

 Bothriocephalidse. Two weak flat suckers ; genital openings usually 

 on the flat surfaces. 



e.g. Bothriocephalus ; Ligula, with no suckers or joints but with 



serial gonads. 



Tetrarhynchidse. With four protrusible proboscides armed with 

 hooks, parasites of fishes. Found also in Sepia. 



e.g. Tetrarhynchus. The finest pearls in the Ceylon pearl oyster 

 are formed round a larval Tetrarhynchus. 



