ON DREPANIDOT^NIA HEMIGNATHI. 615 



The four suckers present no j)eculiarities ; they are deeply 

 cupped, with a small orifice to their lumen, but probably they 

 are capable of considerable change of form (fig. 9). They are 

 probably retracted by some muscle-fibres which cross one 

 another and run into the parenchyma. 



The segmentation of the body begins immediately behind 

 the suckers; at first the segments are very short, but they 

 gradually increase in size throughout the first three quarters 

 of the length of the body. For the last quarter the seg- 

 ments are crowded with embryos ; they become in this region 

 much narrower, more cylindrical in shape, and longer, and 

 are very easily broken off. The posterior free edge of the 

 segments of the anterior two thirds of the body is sharp, and 

 may overlap the segment behind, or may stand out clearly 

 from it. 



The water-vascular system is well developed ; on each side 

 of the body are two longitudinal cauals, — one, the ventral, much 

 bigger than the other, or dorsal. The lining of the former 

 seems to be a structureless cuticle with no cells especially 

 related to it, but the wall of the dorsal vessel is surrounded by 

 a number of small deeply stained cells (fig. 4). I did not see 

 any communication between the vessels of one side, but the 

 larger vessels communicate as usual, one with another, by a 

 transverse vessel running from side to side along the posterior 

 border of each segment. In the head the vessels all com- 

 municate. In some of the better preserved sections such 

 structures as are depicted in fig. 10 were seen : these may or 

 may not be flame-cells; they look rather like them. No 

 valves were seen in the course of the vessels. 



The lateral nerve-cords are well marked, lying externally to 

 the ventral excretory canals ; they fuse together in the head, 

 forming a ganglion which is indicated in fig. 3. No traces of 

 the nerve-ring described by Tower^ as running round the 

 ])Osterior end of each segment of Moniezia, or of the secon- 

 dary nerves described by the same observer, were to be seen. 

 But these, if present, probably require fresh material and 

 1 'Zool. Anz.,' vol. xix, 1896, p. 323. 



