THE DEVELOPMENT OF THE HEAD. 



349 



FIG. 190. Head of Cysticercus pisi- 

 formis, with vascular system. ( x 45.) 



united by a circular vessel into a connected system. Afterwards one 

 can observe the formation of a number 

 of fine twigs, with ramifying processes 

 and ciliated organs. 



At the same time the first cal- 

 careous bodies make their appearance, 

 and that primarily and principally at 

 the point from which the head springs, 

 whence they spread in ever-increasing 

 numbers. Occasionally a few of these 

 concretions are to be found even 

 before this round about the head. 

 The body of the bladder is, as a rule, 

 but sparsely supplied with them, 

 though there are exceptions, such as Piestocystis. 



In order to understand the further development of the head in the 

 tape-worms, one must imagine it as a cylindrical structure, not solid, 

 as it appears, but with a blind cavity running up its whole length. 

 If we suppose this head to pass posteriorly, not into the jointed body 

 of the adult tape-worm, but into a hollow bladder, into which it is 

 indeed iiivaginated, then we have a representa- 

 tion of the primitive state of head in the bladder- 

 worms we are discussing (Fig. 191). The surface 

 of the rudimentary head next the receptacle 

 represents the subsequent inner parenchyma, 

 while the future outer surface, with the cuticle, 

 lines the cavity of the clapper-like rudiment. 

 The tape -worm head thus originates within the 

 bladder, as Goze, and Wagener after him, 

 observed, and occupies an " inverted position." 



One is most distinctly convinced of tin's 

 arrangement by noting the formation of the 

 suckers and hooks which generally appear soon 

 after the first rudiments of the head are formed. They are first seen 

 at the distended lower end of the bottle-shaped cavity, the circle of 

 hooks lowermost, the suckers somewhat higher where the cavity is 

 widest. 1 Their relative position is therefore the reverse of the 

 final one, where the hooks are on the apex above the suckers. 



1 With this agree the results of van Beneden on the development of Cysticercus pisi- 

 formis, as detailed in his " Vers intestinaux," p. 238, 1858. Moniez, however, describes 

 an entirely different mode of formation. I shall afterwards return to the discussion of his 

 theory, but will only here remark that I have repeatedly and most distinctly convinced 

 myself of the truth of my statements. 



FIG. 191. Head of 

 Cysticercus piniformis just 

 mature, (x 40.) 



