FORMATION OF DAUGHTER-BLADDERS FROM BROOD-CAPSULES. 621 



discussed, and also a network of fine threads, which proceeds from the 

 more compact anterior end, and exhibits several distended portions 

 enclosing fatty drop-like structures of various size. The outer cover- 

 ing is formed of a structureless cuticle, which becomes thicker with 

 the increasing size and roundness of the body, and exhibits a lamina- 

 tion which becomes more and more distinct. 



Gradually the internal cavity passes from the posterior to the 

 anterior body. The suckers disappear, the calcareous corpuscles are 

 dissolved, and the parenchyma of the head, and the network which 

 we have mentioned, spread themselves equally over the wall of the 

 body in the form of a fine cellular layer. The circlet of hooks alone 

 reveals the origin of the bladder. But this also disappears when the 

 bladder is about the size of a millet seed, and then the former head 

 does not differ in a single point from a young Uchinococcws-bl&ddeT. 



In cases where the modification of the heads begins in the interior 

 of the brood-capsule (Fig. 331), the latter bursts before the meta- 

 morphosis of the head is completed, 

 so that the young hydatids are all 

 found free within the bladder. 



But it is not only the heads that 

 undergo this metamorphosis, but 

 under some circumstances also the 

 brood-capsules, and especially, it 

 would seem, those which have 

 already lost some of their heads. 

 The transformation begins with a 

 thickening of the hyaline membrane. 

 When this has proceeded so far that 

 the latter possesses the nature and FlG> 332. -Metamorphosis of the 



lamination of a firm CUticle, the brood-capsules into bladders. After 



bladder is set free from its basis. 



The superficial parenchyma disappears, but in place of it a new 

 one orginates in the interior, formed from the substance of the heads, 

 which apply themselves to the cuticle, gradually lose their form, and 

 ultimately become a boundary layer, which is equally distributed 

 over the internal surface. The circlets of hooks, which may at first 

 be perceived in the interior, leave no doubt as to the origin of this 

 inner layer. But afterwards, when these have been destroyed and 

 have disappeared, it is impossible to find any indication of its origin. 

 The bladder then resembles a young Echinococcus, and all the more 

 closely, since the parenchyma again exhibits that reticular marking 

 which we have already often noticed in these bladder- worms. 



In some cases this metamorphosis is somewhat modified, inasmuch 



