402 CYSTIC TAPE- WORMS. 



Cysticercoids, but is more complicated, inasmuch as here we have 

 not only longitudinal and circular muscles, but also a system of radial 

 fibres which run from the middle point of the posterior surface dia- 

 gonally to the side-wall of the bulb (Fig. 234). The latter is further 

 ensheathed by a layer of circular muscles, which have been overlooked 

 by Nitsche, while those running longitudinally are stretched straight 

 between the two surfaces. In contraction these two surfaces would 

 be equally approximated were not the anterior one, 1 which is covered 

 only by the skin, more moveable than the posterior, and therefore 

 more obedient to the action of the muscles. In consequence of this, 

 when the longitudinal and circular muscles are contracted at once, the 

 bulb changes its quiescent form for that of a meniscus, which is open 

 towards the front, so that the hooks seated on the border assume an 

 almost vertical position. But besides the longitudinal muscles, the radial 

 muscles also exert a special force on the anterior surface of the bulb, 

 which arches forwards, and moves the hooks downwards in proportion 

 as the diameter of the posterior half narrows, and as the middle of the 

 posterior surface draws itself inwards in consequence of the funnel- 

 shaped arrangement of the fibres. 



The operation of these radial fibres is further aided by the muscular 

 mass which lies behind the bulb, and which has been compared above 

 to the outer sac of the rostellum in Tcenia undulcda. This comes 

 into action at the same time and presses forward the posterior wall of 

 the bulb, which it surrounds as with a shell. This muscular mass 

 (see Fig. 234) consists of a whole series (six to nine) of discs laid down 

 one over the other, all of a meniscoid shape and surrounded by a com- 

 mon border, which is partly attached to the bulb itself, partly to the 

 subcuticula surrounding it, and is even connected by some of its 

 fibres with the lower roots of the posterior hooks, or rather with the 

 sacs in which they lie. The arrangement of the fibres is, as Nitsche 

 has shown, peculiarly complicated, for they bend in a bow-shaped 

 curve away from the periphery to the centre, and then out again to 

 the periphery, crossing one another in their course through the series 

 of layers. I cannot in any way grant a morphological independence 

 to this muscular mass, especially since its fibres come into frequent 

 connection with the surrounding musculature, and since posteriorly 

 they pass quite continuously into the ordinary muscles of the body. 



We have already noted that the young stages of the cystic tape- 

 worms are characterised by the accumulation of a large quantity of a 

 watery fluid inside an embryonic bladder, which is penetrated by 

 numerous excretory vessels and muscular fibres. In Ecliinococcus the 

 presence of the muscular fibres has been denied, but they are never- 

 theless present, though in small numbers, and feebly developed. 



