NEW ASEXUAL TAPEWOEM. 829 



undovibtedly to the cuticle, and in other cases it appeared to me 

 to be highly probable that the ramifications of these tubes do 

 open on to the exterior here and there ; they at least invade the 

 outermost layer of the cortical tissues. 



The water vascidar tuhes are large in this species, and not far 

 from being equisized. There are, as is the rule, two upon each 

 side of the body. As is so often the case among the Cestodes, the 

 two tubes, instead of being respectively dorsal and ventral and 

 superposed, lie side by side. As is also quite usual among these 

 worms, the two tubes, dorsal and ventral, differ somewhat in 

 sti-ucture. I consider that the slightly smaller and more muscular 

 of the two tubes is the dorsal vessel, from the analogy of other 

 forms ; in the present species, therefore, the dorsal vessel is 

 situated internally to the ventral. They are, however, quite in 

 the same straight line for the most part and also in the same 

 straight line with the nerve-cord. But, as a matter of fact, the 

 more muscular dorsal tube lies in a corkscrew fashion, which is 

 very plain when the proglottids are viewed in longitudinal and 

 sagittal sections, and thus that tube in cross-sections appears to 

 lie now rather dorsal of, and at times rather ventiuUy of, the 

 ventral and more external vessel. Elsewhere they are more 

 directly in the same straight line. It is a remai-kable fact that 

 both of these vessels seem to be quite as large or very nearly so 

 in the most anterior segments of the body. There is no great 

 increase in calibre posteriorly. 



The general relations of these two vessels are shown in text- 

 fig. 114. Text-fig. 115 is a more enlarged representation of the 

 two tubes and the adjacent parts taken from a section of the 

 posterior region of the body. Their detailed structure is there 

 illustrated. In his account of the Oestoidea in Bronn's ' Thier- 

 reichs,' Prof. Braun remarks — " Ob in der Wand der Sammel- 

 rohren auch noch Muskelfaseren vorkommen, ist noch strittig." 

 The figure just refei'red to is, as I think, quite conclusive as to the 

 presence of a particularly thick layer of circular fibres constituting 

 the greater part of the wall of what I regard as the dorsal vessel. 

 This muscular layer appears to wax and wane in thickness from 

 place to place. But it is always thick and thus very apparent. 

 The actual tube is lined with a chitinous cuticle which is also often 

 very thick and everywhere to be seen. Outside of the layer of 

 circular muscles are abundant nuclei, massed round the tube. I 

 did not observe any nuclei among the circular muscular fibres, 

 which are, indeed, very closely contiguous. There appear to be 

 no intrinsic longitudinal muscles to assist in the widening of the 

 tube again after contraction by the circular muscles ; but there is 

 a mechanism which takes the place of such fibres to serve in their 

 stead. 



In the neighbourhood of the dorsal excretory vessel the dorso- 

 ventral muscles form groiips here and there of rather thicker 

 and more closely adpressed fibres, which, as it were, tie to or 

 suspend the dorsal vessel from the cortical layer ; it seems certain 



