40 DE. T. S. COBBOLD ON TREMATODE PARASITES 



phin more or less decomposition of the contents of the intes- 

 tinal tubes has occurred ; consequently the angular appearance 

 of the folds is entirely lost, the margins looking uniformly 

 rounded in profile. 



From the other characters of the worms I cannot bring myself 

 to believe that these flukes from the Ganges are specifically difi'er- 

 ent from those obtained from the Firth of Forth, Nevertheless, 

 in order to make sure that I had not exaggerated the angular 

 character of the intestinal folds as they appeared in my original 

 specimens from the Porpoise, I recently broke up a preserved 

 microscopic slide, and, after soaking the specimens in glycerine, 

 succeeded in bringing the digestive organs well into view, when 

 they displayed precisely the same degree of angulation as the ori- 

 ginal figure in the Society's * Transactions ' shows. There were, 

 however, no traces of rudimentary diverticula, such as I fancied I 

 saw, but did not actually describe, in the original specimens. I 

 now believe that the deceptive appearances were due to the 

 sharpness of the turns or coils of the tubes, which in rather opaque 

 objects is very apt to mislead. This is especially the case with 

 the uterine folds, which, as in the case of Distoma lancea, have 

 been represented as branched when perfectly simple. From a 

 recent examination of my dried specimens of D. crassum I do not 

 feel quite sure that I have not myself fallen into this error. Be 

 that as it may, I desire (on the supposition of an error of inter- 

 pretation of the facts) to restore my Campula ohlonga to the genus 

 Distoma, and I shall therefore in future speak of this parasite as 

 J), campula, retaining the generic as an appropriate specific title. 

 By this change I do not think that the morphological significance 

 of the folded digestive tube is by any means lost. As obtains in the 

 spiral gut of sharks and rays, the object of folding can only be to 

 gain a larger extent of intestinal capacity without incommoding the 

 animal and thereby interfering with its ordinary manner of life. 

 In the members of the genus Fasciola and also in the allied Plana- 

 rians this requirement appears to obtain its maximum. Here, 

 however, even the additional surface gained by a spiral extension 

 of the intestinal tubes appears to be inadequate, since to meet 

 the demand we find the two main channels branched in a most 

 striking manner. 



I cannot here treat of this part of the subject to the extent it 

 deserves ; but in relation to the question of transition-forms I 

 mav remark that an extreme degree of folding seems as if it must, 



