7o6 MacCALLUM. [Vol. XV. 



The intestinal coeca are not pigmented in any of these speci- 

 mens, but the sacculated form is precisely that seen in the adult 

 D. heterostovimn. 



In the specimens marked Clinostomiim heterostomrim, by Stiles 

 and Hassall, the skin is provided with a very delicate armature 

 of spines, but it seems to me, in view of the entire identity of 

 structure in other respects, that this may be a variation due to 

 the difference of hosts, or merely a temporary characteristic, 

 and that this specimen is a different stage of the same form. 



In every other respect these forms are entirely identical with 

 the adult D. heterostovimn, and it will be readily seen that the 

 genital organs as described are precisely what would be expected 

 in the developmental stages of this worm. It is on the ground 

 of this identity in anatomical structure that I should class all 

 these immature forms as developmental stages in the life his- 

 tory of D. heterostomiim. 



Several authors have suggested a close relationship between 

 the adult D. heterosto^mmi and the following other forms : 



D. hians Rudolphi. 

 D. complanatum Rudolphi. 

 D. dimorpJmm Diesing. 

 • D. aquilae Leidy. 



Of these, D. hians and D. complanatnni are readily distin- 

 guished by their having the genital pore in front of the acetab- 

 ulum, and the ovary in front of the anterior testes. 



D. dimorphum is described by Diesing {15) from two hosts, 

 it being found in the muscle, body cavity, and intestine of certain 

 fishes, and again, evidently in a more mature condition, in the 

 mouth of Ardea coqoi and the oesophagus of Ciconia aniericana. 

 The acetabulum is said to be smaller than the anterior sucker ; 

 the mouth terminal ; genitalia are absent in the early stage. 

 In the more adult the genital pore is not far from the caudal 

 extremity. From this description, which seems to be the only 

 one extant, and from his figures it is evident that this worm is 

 closely related to D. heterostomiim; indeed, it cannot be sharply 

 distinguished, but as the original material is not accessible to 

 me, I can go no further than this. 



