DK. T. S. COBBOLB OK THE LARGE HUMAN FLUKE. 291 



fluke are quite unlike those of any of its congeners. This fluke 

 is a remarkably fine species, and, when viewed in the fresh state 

 with a powerful pocket-lens, presents a most striking appearance. 

 •I did not observe any cutaneous spines. I found the eggs to pre- 

 sent an average long diameter of about -^hj'j ^J ijair" ^^ breadth. 

 They are therefore somewhat smaller than those of the common 

 fluke. In the specimen preserved in the Hunterian Museum 

 there was evidence of the presence of an excretory outlet at the 

 caudal extremity ; but in the present examples I did not succeed 

 in finding any trace of the water-vascular system. I have no 

 doubt, however, that it exists in the usual form. 



As regards the affinities of Diefoma crassum, it is clear that 

 this Trematode has little in common either with the liver-fluke 

 of cattle and sheep (^Fasciola Jiepatica), or the still larger species 

 obtained by me from the giraffe {Fasciola gigantea). The simple 

 character of the digestive tubes obviously connects it more closely 

 with the lancet-shaped fluke {Distoma lanceolatum — the last- 

 named parasite being also an occasional resident in the human 

 liver, where its presence has been known to contribute to the pro- 

 duction of a fatal result. Here, I may remark that it has struck 

 me as not a little singular that most of the flukes which take up 

 their residence in the liver exhibit a branched arrangement of 

 the digestive tubes ; and but for the circumstance that the Di- 

 stoma lanceolatum forms a notable exception, I should have been 

 disposed to consider that a branched state of the alimentary 

 apparatus was of necessity associated with this special habita- 

 tion. At all events it is interesting to observe that no species 

 of intestinal fluke is known to display this complex form of di- 

 gestive apparatus, the species before us forming no exception 

 to the rule. In the fluke {Campula oblonga) that I discovered 

 in the liver of a porpoise, there were traces of this tendency 

 of the tubes to branch, whilst an extreme development of this 

 sort is seen in the fluke which proves so destructive to elephants 

 {Fasciola JacJcsoni). Taking the genus Distoma as representing 

 central type forms of the Trematoda, I look upon the flukes that 

 have dendritically branched caeca as aberrant types ; and it is just 

 these particular forms that show the strongest zoological aflBnity 

 with the Planarians, not only by virtue of the anatomical peculi- 

 arity in question, but also as regards their habits. If the contents 

 of the cfBca be examined, epithelium and blood-corpuscles derived 

 from their bearers will be found amongst the debris ; and it is well 



LINN. JOUEN. — ZOOLOGY, VOL. XII 21 



