302 THE ANATOMY OF CESTODES. 



interlaced vessels, lying in the more superficial parenchyma, and 

 partly close under the cuticle. Though not uniformly developed, 

 these vessels are distributed over the whole body, and are connected 

 so frequently and distinctly with the larger stems as to leave 

 no doubt as to the relations of the two systems. The finer vessels 

 obviously form the proper excretory apparatus, being suited to act 

 as simple filters by the structureless nature of their walls, whilst the 

 coarser canals are the efferent ducts. Here and there, doubtless, sub- 

 sidiary functions are discharged ; for example, the abundant develop- 

 ment of the fine network, in the head especially, in forms with com- 

 plex suctorial organs, leads one to conjecture that they act as a sort of 

 corpora cavernosa in the expansion of the suckers. 



As in Bothriocephalus so is it in the other tape-worms, even in 

 Tcenia, as one can observe in fresh clear specimens of say Tcenia 

 elliptica. It is not, indeed, always possible to follow the capillary 

 system for a long distance without interruption, since the individual 

 vessels often seem to disappear and crop up again at other places. 

 Nor are their relations to the longitudinal canals equally distinct 

 throughout. * 



What specially attracts the attention of the observer to this peri- 

 pheral apparatus, is the presence of small, continually waving, cilia- 

 like lappets which are situated on the inner wall of the vessels, 

 especially at the clefts, and which serve to keep up a continuous 

 movement of the fluid, independent of the contractions of the body. 

 In suitable specimens, such as Tcenia elliptica, and especially in 

 Tricenoplwrus, it is not difficult, with a little careful observation and 

 with a high power, to detect these cilia-like lappets, 2 and they have 

 been noticed by v. Siebold. M. Schultze, and others. Their existence 

 has, however, been lately called in question, especially by Steudener. 

 The cause of this mistaken criticism is to be found mainly in the 

 too exclusive examination of sections instead of living animals, and 

 also doubtless in the use of large opaque tape-worms, which, though 

 more readily obtainable for examination, are but little suited for 

 deciding the point in question. 



But not only did the cilia-like apparatus escape observation, but 

 even the capillary vessels in which the former are situated. Longi- 

 tudinal stems and anastomoses were held to represent the whole excre- 



1 It is a striking fact in this connection that the peripheral network cannot be in- 

 jected by way of the longitudinal vessels. This is perhaps due to the existence of valves 

 similar to those at the entrance of the cross vessels. We cannot, however, immediately 

 conclude that there is no communication between the systems. 



2 The discovery of these structures is due to G. Wagener, who has alto earned our 

 approbation by the demonstration of the above-described capillary excretory system ; 

 see " Entwickelung d. Cestoden," loc. cit., p. 14. 



