STUDIES OS THE BCTOPARASITIC TEEMATODES OF JAPAX. Igl 



quence looked much redder than they really were — this species 

 possessing a light flesh-red colour of its own. 



Colouration — Most of the monogenetic Trematodes that I have 

 studied may be described as having a colourless and transparent body ; 

 but since the internal organs are more or less visible from the exterior 

 the body appears coloured. The only real exceptions in this respect 

 that I have observed are Tristomum sinuatum and T. rotimdiun, which 

 possess, as just mentioned, a light flesh -red colour of their own; but 

 in which tissue of the worm this colour is lodged I have not been able 

 to make out ; possibly it may be in the investing membrane. The 

 specimens of Hexacotyle acuta that I have myself collected had all a 

 dusky colour like that of the gill of its host, but those that were 

 collected by my friend Mr. Nozawa were perfectly colourless except 

 where the vitellarium was seen through, which is in this species more 

 or less dusky coloured. I therefore believe that the generally dusky 

 colour of my specimens was due to a greater development of the 

 vitellarium. 



The only internal organs that possess any colour of their own are 

 the vitellarium and the pigment cells of the intestine already describ- 

 ed. In fresh specimens the former looks dark and granular by 

 incident light, and slightly yellowish by transmitted light ; while 

 the pigment cells of the intestine look dark brown or perfectly black 

 by both incident and transmitted light. The body of most ecto- 

 parasitic Trematodes being thus transparent and allowing the substra- 

 tum to be seen through — for the vitellarium is in fresh specimens 

 not conspicuously dark, and the intestinal pigment-cells are not close 

 enough to each other to constitute a single visible object — -they are some- 

 what difficult to detect at first sight. This, however, must not be 

 regarded as a case of protective colouration ; for in the first place, the 

 nature of the habitat already protects the parasites from being at- 



