204 ON THE ANATOMY OF ECHINOCOCCUS VETERINORUM 



ance of the two being more markedly different than even the figure 

 represents it. 



I cannot help thinking that these withered EcJiinococci, for that, 

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

 Erasmus Wilson has figured as developing forms {loc. 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 Ecliinococci. — These, in various stages of development, 

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

 diagrams E. and F. (PI. XXIX. [Plate 22]). 



Elongated elevations of the endocyst (PI. XXVIII. [Plate 21] fig.5) 

 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 Echinococ- 

 cus, 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 set free. The pedicle contracts upon itself so as to 

 have a rounded form, but it very often betrays its previous adherence 

 by the ragged fragments of the endocyst, which it carries with it. 



Whether this is properly a normal process in the Echinococcus it 

 is difficult to say, but as Dr. Guido Wagner ar d Van Beneden have 

 shown, it occurs normally in the Tetrarhyncnidce, and it exactly re- 

 sembles that detachment of the " tail " from the Cercaria, which takes 

 place in the Distomata. 



As little is it known whether the Ecliinococci undergo any further 

 development. The suggestion first made by Delle Chiaje, that they 

 may dilate into cysts and develope young Ecliinococci within them- 

 selves, appears to me highly improbable ; and it is an hypothesis 

 which is not needed to account for the secondary cysts. 



b. Fixed Secondary Cysts. — The development of these indeed, 

 takes place in such a manner as to preserve the homological relations 

 of the EcJiinococci to the exterior of the parent. The secondary cysts, 

 in fact, are thus formed : Ecliinococci are developed not only from the 

 inner surface of the endocyst, but from its outer surface (PI. XXVIII. 

 [Plate 21] fig. 4). Their growth is probably accompanied by that of 

 the endocyst itself, which thus becomes raised up from the ectocyst 

 and projects into the general cavity (fig. 5). Of course any internal 

 Echinococci which happen to be attached to this part of the endocyst 

 are raised up with it (figs. 4, 5): they may be fewer or more according 



