CONTRIBUTIONS TO THE ANATOMY OF THE HIR[JDINEA. 499 



organised nerve-cord lying in a much less highly organised 

 coelom^ and of well-developed funnels to the nephridia, all point 

 to this. The Leeches have thus had an ancestor which in 

 possessing a coelom was already a great advance upon any 

 Platyhelminth form — if we accept, as I cannot yet do, Lang's 

 views of the coelenterate character of Platyhelminths. 



Lang^ has put forward the view that the paired diverticula 

 of the alimentary canal in Leeches are homologous with the 

 coelomic diverticula of the ancestral alimentary canal of the 

 Enterocoela, and thus compares them with the diverticula of 

 the alimentary canal of the Triclada ; but as it is probable, 

 that in Leeches the coelom is represented by a very different 

 system of spaces, such diverticula cannot have the special con- 

 nection with the diverticula in the Triclada which Lang sug- 

 gests, unless the latter too do not really represent coelomic 

 diverticula, — a representation which Lang has suggested rather 

 than proved. 



The consideration of the anatomical facts now ascertained 

 with regard to the adult forms of the various genera of Leeches 

 appears to me, in the absence of more definite embryological 

 information than we possess, to lead us to no very certain con- 

 clusion as to the affinities of this group. Everything in this 

 question depends on a perfectly reliable knowledge of the 

 embryological history, in the different genera of Leeches, of the 

 spaces which I have treated of in this memoir under the name 

 *' coelom," and a simultaneous knowledge (more complete than 

 that which we owe to Lang) of the embryological history of 

 the intestinal coeca and nephridia of Planarians and Trema- 

 todes, and of the presence or absence of a temporary ''coelom" 

 in the embryonic condition of the latter. 



Assuming for the moment that Lang is right as to the 

 definite coelenterate structure of the Planarians and Trema- 

 todes, and that such structure is not a degeneration but a 

 primary character, then it would be necessary to place the 

 Leeches in a distinct group, characterised by its " coelom ^' into 

 which the large nephridial funnels open, by its vascular system, 

 1 ' Mitthl. Zool. Stat. Neapel.,' Bd. 3, p. 233. 



