384 Zoological Society. 



clearly seen at the edge of a cyst. They terminated in a some- 

 what wide space at the base of the pedicle of each contained Echino- 

 coccus, and in one instance I traced a vessel for some distance into 

 this pedicle. There were no cilia nor granules contained in these ves- 

 sels, but they precisely resemble those canals of which traces were 

 seen in the Endocyst, and their development will, I think, show that 

 they are identical with them. 



I may anticipate so far as to say that I believe that these vessels 

 represent the water vascular system of the parent-cyst. 



When such a sac as this is burst the Echinococci become everted, 

 and the secondary cyst turns itself inside out, so that the Echinococci 

 appear to be seated like Polypes upon a central stem. This curious 

 peculiarity has led to much misconception as to the mode of their 

 attachment ivithin the cyst. Von Siebold, however, pointed out the 

 true nature of this process as far back as 1837* (vide infra). 



The smallest free secondary cysts varied in size, as I have said, 

 down to T |oth of an inch, when they contained only four Echinococci. 

 These, however, were quite as large as those in the largest secondary 

 cysts. 



The structure of the middle-sized and small vesicles was in most 

 respects the same as that of the large ones, but there was this differ- 

 ence, that they possessed, attached to their outer surface, by pedicles, 

 a variable number of oval bodies of the same average size as the 

 Echinococci or less, but presenting a yellow wrinkled appearance, 

 containing very few corpuscles, often none, and either exhibiting no 

 trace of the circlet of hooks, or offering only a few, dark irregular 

 and withered-looking ones. It was impossible to confound these 

 external bodies with accidentally everted internal heads, the appear- 

 ance of the two being markedly different. 



I cannot help thinking that these withered Echinococci — for that, 

 as will be seen presently, is what they really are — are what Mr. Eras- 

 mus Wilson has figured as developing forms {Joe. cit.). 



Development. — We have found free Echinococci and free secondary 

 cysts contained in the fluid of the primary cyst : how do they come 

 there ? To answer this question we must return to the endocyst. I 

 found adherent to, and growing from it, a. fixed Echinococci, and 

 b. fixed secondary cysts. 



a. Fixed Echinococci. — These, in various stages of development, 

 are scattered all over the inner surface of the endocyst, as in the 

 diagrams E. and F. Plate XI. 



Elongated elevations of the endocyst are first seen : within these 

 the circlet of hooks and then the corpuscles make their appearance : 

 the elevation becomes a papilla, and the papilla, gradually constricting 

 itself at the base, becomes the oval Echinococcus, attached by a 

 narrow pedicle. In this state the slightest touch is sufficient to 

 separate the pedicle from the endocyst, and then the Echinococcus is 



* The Echinococci are figured in this everted state by Chemnitz (quoted by 

 Siebold, art. Parasiten, Wagner's Encyclopaedia. &c), by Erasmus Wilson (Medico- 

 Chir. Transactions, 18 15), and by Busk (Microscopical Transactions, 1846). 



