12 DR. F. B. BEDDARD OX 



the scolex. It is not impossible that we have here an intermediate 

 state of affairs, where a true sucker (acetabulum), originally only 

 an accessoiy structure (as has been held), has nearly comj^letely 

 replaced the phyllidium, of which comparatively small traces 

 remain. In connection with this matter, it must be borne in 

 mind that the systematic position of the genus Ichthyotcenia is 

 not yet settled. Some place it in a family, Ichthyotseniidae of the 

 group Tetraphyllidea ; while Lonnberg * dwells upon its likeness 

 to Tetrahothrmm, and Liihe t places the certainly closely allied if 

 not congeneric Cre2yidohothriuin gerrardi also in the genus Tetra- 

 bothrium. 



The muscles which move the scolex are well developed in this 

 species, but by no means so prominent as in the last species. 

 This is remarkable when we consider that Ichthyotcenia nilotica 

 is the larger of the two species. On the other hand, I have no 

 information as to the mobility of the scolex in the present worm. 

 Immediately behind the scolex these muscles are massed into 

 regular and, of coui'se, longitudinally running bundles of fibres, 

 which are not so large as are those of the last, and therefore do 

 not contain so many individual fibres. These biuidles lie below 

 the subcuticular layer, and occupy exactly the position in which 

 the longitudinal fibres of other species of Ichthyotoinia are repre- 

 sented by Schwarz. But in the present species, as in the last, 

 they only exist, and for a very short length, in the part of the 

 body immediately following the scolex. I counted ten of these 

 bundles in a section in the neck-region, only just behind the 

 scolex ; they form a complete ring, and thus lie without as well 

 as within the water-vascular tubes. Further back the bundles 

 decrease in number, and in mature segments are not recognisable. 

 The greatest number of fibres in a bundle is 7 or 8. 



The structures seen in a transverse section of a proglottid (text- 

 fig. 3) are not different from those of other species of this genus 

 which I describe in the present paper. The delicate layer of longi- 

 tudinal fibres below the cuticle is plain and also the very strongly 

 marked subcuticular layer of darkly staining cells. I covild find no 

 longitudinal muscular layer beneath this, nor is there any boundary 

 line that I could discover between the cortical and medullary 

 parenchyma. Calcareous bodies were very evident here and there. 

 The water-vasctdar tubes are very plain in the anterior region as 

 two tubes on each side. These are not very difierent in calibre, 

 and the dorsal and ventral of each side were more or less accu- 

 rately superposed. In the mature segments I can find only one 

 tube on each side, which I am inclined, mainly on account of its 

 small size, to regard as the dorsal water-vascular tube. In longi- 

 tudinal horizontal sections I could detect no evidence of more 

 than a single water-vascular vessel on each side. I have also 

 been unable to find any branching of this tube to join the 

 corresponding vessel on the opposite side of the body. A single 



* Ceiitralbl. Bakt. u. Paras, xv. 1894, p. 801. 



t In a footnote to a pai^ev, " Zuv Kenntniss einiger Distomen," Zool. Anz. 1899. 



