834 DR. p. E. BEDDARD ON A 



larger than that of the other and is relatively asymmetrically 

 placed. This latter fact is doubtless due to the bundles of longi- 

 tudinal fibres surrounding the large lateral tubular organ. This 

 structure has, as it were, pushed the nerve-cord and the water 

 vascular tube of its side towards the centre of the body. Indeed, 

 the vessel in question lies very nearly in the actual centre of the 

 section and quite in this position shortly before and during its 

 connection by the transverse vessel with the tube of the opposite 

 side of the body. These transverse vessels are at regular intervals 

 and quite easy to see as in the adult worm. I did not observe 

 any other branches of the water vascular tubes than these. 



These sections from the middle of the body of the young worm 

 also show very plainly the remarkable constitution of the nervous 

 system in this Cestode. One of the two lateral cords (text- 

 fig. 1 16, 7^) is very obvious indeed, lying between the water vascular 

 tube of that side and the tubular organ of doubtful meaning. 

 It cannot possibly be missed in these sections. But on the opposite 

 side of the body I could find no trace whatever of any nerve-cord 

 even of smaller size than the one represented in the text-figure. 

 I feel confident that a failure to observe a cord in this situation, 

 were it present, would be difficult. The medullary tissue is so 

 clearly difierentiated by the stain (iron hsematoxylin *) that 

 the nerve-cord, if of any size at all comparable to that of the 

 opposite side of the body, would stand out quite prominently. 

 This state of afi'airs is undoubtedly very anomalous and hard of 

 explanation. For we shall see later that the two nerve-cords are 

 both quite recognisable towards the end of the body. 



Finally, this transverse section shows to one side a large tube 

 cut across, to which reference has been made incidentally once or 

 twice already. It is situated in the centre of a group of bundles 

 of longitudinal fibres, which bundles are like those in the cortical 

 layer of the body in every way, including their rather sparse 

 scattering round the centrally placed tube. The bundles in the 

 cortical layer are not densely pressed together as they are, for 

 example, in Dasyurotcenia rohusta f. The tube itself is of con- 

 siderable size and is lined by a thick layer of chitin, which is 

 stained precisely like the chitin which covers the body of the 

 worm externally. Outside of this is a single layer of stout longi- 

 tudinal muscle-fibres, and then a deeply staining layer of elongated 

 cells, interspersed among which are small bundles of stout longi- 

 tudinal fibres. The structure of the tube is in fact almost exactly 

 that of the outer layer of the body, only difiering, indeed, by the 

 intercalation of the groups of stout longitudinal fibres among 

 the cells. 



We shall now consider the course and structure of this tubular 

 organ throughout the body of the young worm. The identity of 

 structure with the outer layer of the body which this tube 

 shows in the middle region of the body, is rendered intelligible 



* 1 am indebted to Dr. Plimmei-, F.R.S., for the use of this reagent. 

 t See Beddard, P. Z. S. 1912, p. 684, test-fig. 97, l.m. 



