344 THE DEVELOPMENT OF CESTODES. 



Almost contemporaneously with the differentiation of the cortical 

 cells, a new formation occurs in the peripheral tissue. In some way 

 not clearly understood, there arises in that region what we have 

 already discussed in the adult tape-worm as the excretory system. 1 

 Here and there one observes a clear, usually stellate, finely branched 

 streak, in which one can afterwards detect the parts of a vascular 

 network which surrounds the whole bladder, and rapidly attains a 

 considerable development. But before the formation of the head, it 

 is not possible to distinguish longitudinal and transverse vessels ; it is 

 simply a network with meshes of varying size and diverse arrange- 

 ment. From the larger stems, there spring numerous fine branches 

 ramifying like a tree, which apply themselves to the surface of the 

 bladder, and pass between the fibrils into a second finer network (see 

 Fig. 199). No communication with the watery internal space is 

 observable. On the other hand, we can recognise in the peripheral 

 vessels the same ciliated apparatus which we noted in the vascular 

 system of the adult Cestodes. They are exceedingly numerous in 

 Cysticercus pisiformis, and are in continual undulating motion. I 

 have not been able to decide whether the cilia are seated on the 

 ordinary walls of the vessels, or on special funnels appended to 

 the vessels, and in connection with cavities in the connective sub- 

 stance. 2 The latter is supposed to be true in the case of young Dis- 

 tomes. At any rate this apparatus in the bladder must have the 

 same significance as in the adult Cestodes. The resemblance becomes 

 still more complete when we learn from Wagener that the vascular 

 system even in the bladder- worm communicates with the exterior by 

 means of a short contractile tube at the posterior pole. 



I have been able to convince myself of the existence of this ter- 

 minal funnel only in the above-mentioned hookless Cysticercus from 

 Lacerta vivipara (Fig. 1 85). It is clad with a thickish cuticle, pro- 

 bably resulting from an invagi nation, and leads to two (or four?) 

 vessels which ascend to the head at some distance from the surface, 

 and give off in their course numerous lateral branches. 



The young bladder-worm persists for a while as a simple more or 

 less spherical watery bladder, until the formation of the subsequent 

 tape-worm head inaugurates a new epoch. In Echinococcus this takes 

 place only after several months, when the bladder has grown to per- 

 haps the size of a nut ; in the Ccenurus it occurs in the fifth week, 

 when the worm is as large as a pea; in the Cysticercus proper it 



1 In my monographs on cystic worms, I erroneously referred the appearance of this 

 vascular system in Cysticercus pisiformis to a later developmental stage. 



2 Biitschli, " Bemerkungen iiber den excretorischen Gefassapparat der Trematoden, " 

 Zool. Anzeiger, Jahrg. ii, p. 588, 1879; see also the first German edition of this work, 

 Bd. i., p. 766. 



