HYDATIDS. 117 
are developed in a single segment (proglottis). The six- 
hooked embryos develop, are expelled from the dog, and 
find their way in drinking-water or in food into the human 
intestines, whence they bore into the liver, their favorite 
habitat, or are carried along the blood-vessels into some 
other organ, where they develop into bladder-like bodies 
called acephalocysts or hydatids. In its 
earliest stages the hydatid is spherical and 
surrounded by a capsule of condensed con- 
nective tissue of its host. By the fourth 
week the young 7. echinococcus is one half 
a millimetre (one-fiftieth inch) in length, 
and it is probably many months before the {t 
Echinococci heads are entirely developed. 
When this stage is reached the tape-worms 
become sexually mature in from seven to 
nine weeks after, when the milk-white 
worms may usually be found embedded in 
the mucus of the duodenum and upper 
part of the small intestines, with their 
heads attached to the villous surface of 
~the intestine. The hydatids or cysts in 
which the Echinococci develop are of 
three kinds—viz., exogenous, endogenous, 
and multilocular, and lie embedded in the 
parenchym of the liver, etc., and are filled 
with a clear amber-colored fluid. The 
Echinococcus heads, first on the inner sur- 
face of the cyst and in the interior of the 
Echinococcus-head (brood-capsule), devel- 
ops a second brood of scolices, contained 
Fig. 78. — Tenia 
in a secondary cyst. Finally, a tertiary echinococeus. — After 
cyst, containing tertiary or granddaughter ®"°* 
scolices, arises. Sometimes the secondary hydatids will de- 
velop scolices and granddaughter vesicles before the original 
maternal hydatid has acquired Echinococcus heads (Cob- 
bold). 
The largest human tape-worm is Bothriocephalus latus 
Bremser (Fig. 79). 
