NEPHRIDIA OF CERTAIN EARTHWORMS. 405 



coelom perforating the mesentery which separates the first 

 from the second segment; 1 hence Bergh's objection to the 

 homology between the larval and permanent nephridia, on the 

 score that the former do not lie in the true coelorn, is removed. 



It is not yet a universal belief that a ccelom is absent in 

 the Platyhelminths ; in any case, as Lang says, " the entire 

 mesoderm of the Platyhelminths may very well be the equiva- 

 lent of the entire mesoderm in the Enterocoela," apart 

 altogether from the question of the enclosed cavity. In 

 Capitellidse the nephridia seem, from Eisig's description, to lie 

 in the somatopleure, i. e. not in the coelomic cavity at all. 

 The greater portion of the nephridium in Polygordius is 

 similarly situated ; and Fraipont in his work upon the Archi- 

 annelida (9) remarks upon this as an archaic character. 

 Again, Weldon (14) has brought forward reasons for believing 

 that in Dinophilus, "which is literally no more than a larval 

 Annelid with reproductive organs " (Lang), the body cavity 

 may be really strictly comparable with that of Annelids, seeing 

 that in S a c c o c i r r u s — an undoub ted Annelid — the body cavity 

 may be secondarily (?) invaded by a ramifying network of 

 mesodermic cells. 



In Dinophilus there are excretory organs of the Platy- 

 helminth type, branched and ending in flame cells, which are 

 in D. gyrociliatus (according to Ed. Meyer, quoted by 

 Lang) metamerically arranged, with a pair of external aper- 

 tures to each segment. These facts taken together appear to 

 me to do away with many of the difficulties urged by Bergh 

 against the comparison of the Platy helminth and Annelid 

 excretory system. 



A difficulty in comparing the Platyhelminth with the 

 Annelid excretory system is undoubtedly in certain structural 

 differences ; there is no trace in any Platyhelminth of a 

 " funnel ;" the excretory tubules end in the well-known 

 "flame cells." This difficulty has led Lang (11) to regard the 

 funnel in the Annelid as a new structure unrepresented in the 

 Platyhelminths ; this opinion is supported by the observations 

 1 Vejdovsky (13), pi. XVI, fig. G. 



