EYDATIDS. 



159 



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 

 surronnded by a capsule of condensed con- 

 nective tissue of its host. By the fourth 

 week the young T. ecMnococcus is one half 

 a millimetre (one-fiftieth inch) in length, 

 and it is probably many months before the 

 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 

 in a secondary cyst. Finally, a tertiary ecMmmccus .~-'''ai^i: 

 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 Bothriocephahis latus 

 Bremser (Fig. 109). 



