HY'DATID (Gk. iffaric, hydatis, water vesicle, hydatid, from iAidp, hyd6r: water; con nected with OChureh Slay. rode, Skt. udan, water, and ultimately with Goth. zrato. OHG. trazzor, Ger. 11'asser, AS. tetrter, Eng. water ; AS. Iraq, Eng. met ; 011G. of tar, Ger. Ot ter, AS. otor, Eng. otter). The bladder-worm. It is allied to the tapeworm, but differs in being bladder-like, and similar in shape to the `eysticerens' of the tapeworm. The heads bud on special brood capsules in such a may that their invagination is turned toward the cavity of the vesicle. About 50ou eggs are developed in a single segment (proglottis). The six-hooked embryos develop, are expelled from the dog, the first host, and find their way in drinking-water or in food into the human inte,tincs, whence they bore into the liver, their favorite habitat, or are carried along the Hood-vessels into some other organ, where they develop into bladder-like bodies or ( EchinOel lre ifcr echinocoecus). Ily the fourth week the young is I. nun. (I.50 inch) in length, and it is probably many months before the cehi noeoecus heads are entirely deNeloped. The worms become sexually mature in from seven to nine weeks after this stage is reached, when the milk-white worms may usually be found im bedded 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 parent vesicle may grow as large as n man's head. The cyst in which the bladder-worn, lies, and which is caused by it, is called a 'hydatid cyst.' There are two forms of this hydatid, one (Echinocoecifer ho minis) living in man, and the other (Echinocorcifcr relerinorum) in domestic animals. When these cehinococcus cysts remain sterile, as they frequently do, they are called 'acephalocysts.' "Another, and indeed pathologi cal form," says Sedgwick, "is the so-called 'mul tilocular* echinococens, which was for a long time taken for a colloid cancer. It is also found in manunalia (in cattle), and here presents a confusing resemblance ton mass of tubercles. The eehinoeoccus disease (hydatid ).lague) was wide ly spread in Iceland. This disease, likewise, seems endemic in many places in Australia."