622 VARIOUS FORMS OF ECHINOCOCCUS. 



as it affects not the whole brood-capsule, but only a certain part of it, 

 which is then at an early stage marked off from the rest by a 

 constriction. 



According to Easmussen, however, the laminated cuticle of the 

 secondary hydatids does not originate by the thickening of the hyaline 

 inner membrane, but upon the external surface of the brood-capsule, 

 which from the first is covered by a delicate cuticular layer. The 

 metamorphosis of the brood-capsules into hydatids would accordingly 

 be a kind of encapsulation, as was indeed previously asserted by 

 Eschricht. Any change of the parenchymal sheath would thus be 

 unnecessary, and its formation would be independent of the destruc- 

 tion of the heads, which in its turn would be a process of only 

 subordinate importance. 



When once they have arisen, the secondary hydatids are also able 

 to multiply by external buds, and that in the very same way as we 

 have described in the simple Uchinococcus. The investigations of 

 Davaine, as well as those of Levison and Easmussen, leave no doubt 

 regarding this point. The latter saw the proliferation even in hydatids 

 which hardly measured half a millimetre, while Davaine observed it 

 in older and larger daughter-bladders. 



It has already been mentioned that the secondary hydatids also 

 correspond to the simple ^cAmococcMs-bladders, as regards the pro- 

 duction of brood-capsules and heads. By this vesicular metamorphosis 

 these bladders can of course again produce hydatids in their interior, 

 so that three generations are then enclosed one within the other. 

 Even in sterile hydatids one sometimes finds granddaughter-bladders, 

 but it would seem that these owe their origin to no new formation, 

 but to certain heads which undergo their vesicular metamorphosis at 

 the same time as the enveloping germ-capsules, and without leaviag 

 them. Naunyn mentions that he has often found such heads in the 

 interior of small hydatids which had been newly formed from brood- 

 capsules. 



If, however, the secondary hydatids all originated in the way which 

 we have described, as the results of the metamorphosis of the heads 

 and germ-capsules (and against this view there are no d priori con- 

 siderations, since both structures are morphologically perfectly equi- 

 valent^ to the bladder), then there could of course be no sterile 

 Echinococci with daughter-bladders in their interior. The Echinococcus 



* I may take this opportunity of mentioning that very often structures of the same 

 morphological value undergo a subsequent transformation. We know, for example, that 

 in crabs the swimming legs are transformed in the course of the metamorphosis into 

 mouth-appendages, and are functionally replaced by others subsequently formed. We also 

 know that the nutritive polyps of certain Tubularidte modify their former structure from 

 external and internal causes, and change into proliferating individuals (Blastostyles). 



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