ECHINOCOCCUS HYDATIDS 249 



month after reaching their destination in the liver or other organs 

 they are in the form of little globular bodies, enclosed by a cap- 

 sule produced at the expense of the host. A cyst measures about 

 one mm. ( s of an inch) in diameter. By the end of the fifth 



FIG. 95. Diagram of portion of small Echinococcus cyst showing daughter cyst 

 (d.c.), brood capsules (br. cap.) and invaginated heads (h.). X about 5. 



month it has grown to the size of a walnut. The membrane of 

 the bladderworm itself is very delicate, but the capsule formed 

 by the host is thick and tough. The enclosed fluid is transparent 

 and nearly colorless, and is composed of various materials which 

 have permeated in from the blood and tis- 

 sues of the host, and of the waste products 

 produced by the growth of the parasite. 



When the hydatid has reached this stage 

 in its development (Fig. 95) there grow 

 into its cavity from the inner surface little 

 vesicles or brood capsules, on the inner sur- 

 face of which in turn there grow a number of 

 little heads or scoleces. Each of the heads 

 has the power ultimately to grow into an 

 adult worm. As there may be a dozen or 



,. , r i v i i i FIG. 96. Multilocular 



more of the scolex-bearmg brood capsules in cyst from i iver O f steer> | 

 a single hydatid, and from six to 30 heads nat.size. (After Ostertag 

 in a single vesicle, the number of heads of fl 

 scoleces produces may be enormous. Sometimes there may be 

 still further multiplication by the development of secondary cysts 

 either inside or outside of the original hydatid which may develop 

 a whole series of scolex-bearing vesicles of their own. 



Sometimes instead of forming the usual large vesicles and 

 secondary vesicles, the growth results in the formation of a great 

 mass of small separate vesicles (Fig. 96), varying in size from a 



