162 G. A. and W. G. MacCallum, 



assumes a veiy wavy or zigzag course, the surrounding cells becoming 

 more compactly and closely applied about it. Even where the 

 mantle of cells is thickest the lumen can be seen shining through 

 as an empty tube. It extends back only a short way, not more 

 than four or five millimeters to a point about midway aloug the 

 Stretch of the testes where it becomes invisible. In the section it 

 is seen, hovvever, that it does not end here but passes into an 

 extremelj' thinwalled tube. In spite of our best efforts we have 

 not succeedel in tracing this continuation backward nor determining 

 absolutely whether it divides or not. This is partly because its 

 wall loses any distinctive character and becomes exactly like that 

 of the wide and tortuous excretory canals which are present every- 

 where throughout the length of the body. 



The anterior or mouth sucker is terminal and surrounded by 

 no lip or Prolongation. It is quite strong being provided with an 

 inner and outer layer of circular as well as the main mass of 

 radial fibers. Numerous large cells are embedded in this muscle and 

 there is a fairly thick cuticular lining which passes on into the 

 Pharynx. This has a wall made up of a loose network of radial 

 fibers and also shows large cells embedded in it. The Oesophagus 

 is a thin walled tube lined by a smooth membrane. Possibly the 

 whole succeeding tube should be regarded as the Oesophagus if it 

 should ever prove that the thin walled sac at its end is bifurcated 

 or that it represents the definite intestine. The lining membrane 

 gradually thickens as we pass into this convoluted tube and becomes 

 closely set with cilia but no lining epithelial cells are to be seen. 

 Outside this membrane, however, the cells are ranged in radial 

 Strands closely packed about the canal but fraying out a little 

 externall3\ They are narrow elongated cells with very definite 

 nucleus and are at least ten or twelve deep all round the canal. 

 It is hard to know exactly how to explain their presence and what 

 function to ascribe to them. At the lower end these cells fade 

 away and the ciliated lining disappears. — There is left only the 

 most delicate membrane in which cellular structure cannot be made 

 out clearly. 



The nervous System consists of a pair of ganglia with commis- 

 sural connection just behind the pharynx and several rather stout 

 nerve trunks which run to the anterior end of the body and backward. 



The excretory system appears to be composed of two large thin 

 walled tubes which run from one end of the body to the other. 



