THE SIMPLE FORM OF ECHINOCOCCUS. 613 



5 mm., or even double that, and acquires a quite extraordinary firm- 

 ness. It possesses its own arteries and veins, which spring from the 

 neighbouring vessels, and are connected by a rich capillary network. 

 On the smooth internal surface it bears at first a thin layer, which is 

 fastened almost as firmly to the Jc^m0c0cczS-membrane as to the 

 surrounding wall of the cyst, and which, on microscopic investigation, 

 is seen to be the cellular deposit already repeatedly mentioned. 



As to the form of the Echinococcus, it is usually spherical (Fig. 317), 

 but there are also bladders which possess an oval form, or by unequal 

 development of the surface have become more or less bulging, as is to 

 be seen in the adjoining representation. As a rule, such irregular 

 forms find their explanation in the character of the connective-tissue 

 cyst and its surroundings. They arise when the growing bladder 

 encounters obstacles of varying strength. 



FIG. 329. Bulging Echinococcus in its natural size and position. 



The fluid which fills the internal cavity of the JZchinococcus-bl&ddeY 

 has commonly a clear watery character. It is not coagulated either 

 by boiling or by application of acids, and has in its fresh state no 

 corpuscular contents. The brood-capsules and fichinococcus-he&ds, 

 which the older observers saw swimming freely in this fluid, are in 

 fresh specimens all attached to the internal surface. They shine 

 through the body-parenchyma, which is usually transparent, though 

 occasionally turbid at isolated spots, or even throughout. 



The brood-capsules produced by these EcJiinococci have been 

 already claimed as daughter-bladders, and, indeed, proliferating 

 daughter-bladders. But they do not represent the only form of 

 daughter-bladder which these worms can produce. Beside these, 

 there not unfrequently appear other daughter-bladders, which possess 

 exactly the structure and nature of an ordinary Echinococcus, yet do 



