CESTODA. 195 
a scolex or head, which, in another host, buds off the chain of proglotdzdes. 
As it is virtually the same animal throughout, the life history does not 
include an ‘‘alternation of generations.” It is doubtful, however, what 
term should be applied to those cases in which the bladder-worm 
(Cenurus 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 sieboldiz, a simple cestode which is sexual within the small 
fresh-water oligocheet Tud¢fex rivulorum. 
Representative Life Histories. 
ADULT, SEXUAL, OR TAPE-WORM 
STAGE. 
Non-SEXuAL, PROSCOLEX, OR BLADDER- 
WORM STAGE. 
1. Tenia solium, in man, with four 
suckers and many hooks. 
2. Tenia saginataor mediocanellata, 
in man, with four suckers, but no hooks. 
3. Bothriocephalus latus, in man, 
with two lateral suckers, but no hooks, 
with less distinct separation of the pro- 
glottides than in Zenia. It may be 
ir yards in length, 
4. Tania (Echinococcifer) echino- 
coccus, in dog. Very small, with three 
joints. 
5. Tenia cenurus, in dog. 
6. Tenia serrata, in dog. 
7. Tenia cucumerina, in cat. 
1. Cysticercus cellulose, in muscles of 
the pig. 
2. Bladder-worm in cattle. 
3. Theciliated,free-swimming embryo 
becomes a parasite in the pike, trout, 
burbot, etc., but without a distinct 
bladder-like stage. 
4. Echinococcus veterinorum, in 
sheep, cattle, pigs, etc., and some- 
times in man, producing brood cap- 
sules, which give rise to many “‘ heads.” 
5. Canurus cerebralis causing sturdie 
or staggers in sheep, with numerous 
“heads.” Also in cattle, goat, horse, 
etc. 
6. Cysticercus pisiformis, 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 :— 
Cestodariidze. No joints, one set of gonads. 
eg. Archigetes, Caryophylleus, Amphilina, Gyrocotyle. 
Bothriocephalide. Two weak flat suckers ; genital openings usually 
on the flat surfaces. 
e.g. Bothriocephalus ; Ligula, with no suckers or joints but with 
serial gonads. 
Tetrarhynchide. With four protrusible proboscides armed with 
hooks, parasites of fishes, Found also in Sefza. 
e.g. Tetrarhynchys. The finest pearls in the Ceylon pearl oyster 
are formed round a larval Zetrarhynchus. 
