NEW ASKXUAJj TAiMCWORM. 829 



undoubtedly to the cuticle, niid in other cases it appeared to me 

 to be highly probable that the raniilications 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 vascular tubes are large in this species, and not far 

 from being ecpiisized. There are, as is ihe rule, two u})on each 

 side of the body. As is so often the ca,se a,mongthe 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, diiler somewhat in 

 structur(\ ] consider that the slightly snuilier and more nuis(!ular 

 of the two tubes is the dorsal vessel, from the analogy of othcM- 

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

 situated internally tt) the ventrnl. They are, however, quite in 

 the same straight line for the most part a.nd 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 tl>e proglottids are viewed in longitudinal and 

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

 lie now ralliei- dorsal of, and a,t times rather vcMitiully of, the 

 ventral and more external vessel. Elsewhere tlu>y are more 

 directly in the same straight line. It is a rema,rka,bl(^ fact tlwil, 

 both of these vessc^Is seem to be (]uite a,s large or very nearly so 

 in tlie most anterior segments of (lie Ixxly. ^Phere is no great 

 increase in calibre posteriorly. 



The general relations of these two vess(^ls are shown in text- 

 lig. 114. Textlig. 11 f) is a more enlarged repi-esentallon of the 

 two tubes and the a,djacent parts takcMi from a section of the 

 posterior region of the body. 'I.Mieir detailed structure is tluu'e 

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

 reichs,' I'rof. Brami remarks - " Ob in der Wand der Hammel- 

 rohren auch noch Muskelfaseren vorkonunen, ist noch strittig." 

 The figure just referred to is, as I think, quite conclusive as to the 

 presence of a parfcicul'irly thick layer of circular fibres constituting 

 the grea^ter part of the wall of wha,t 1 rega,rd as the dorsal vessel. 

 This muscula,r layer appears to wa,x and vva,ne in thickness from 

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

 The actual tube is lined withachitinous cuticle which "is also often 

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

 circular muscles are al)iuulant nuclei, massed rotuul the tube, i 

 did not observe any nuclei among the circular muscular fibres, 

 which a.re, ind(!ed, very closely contiguous. There appear to be 

 no intrinsic longitudinal nuiscjies to assist in the widening of tlui 

 tube again after conti'a,ctiou 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 groups here and there" of ra.ther thicker 

 and more closely adpressed fibres, which, as it wc^re, tie to or 

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



