408 FKANK E. BEDDAKD. 



Annelida have been derived from at least two Platyhelniintk 

 ancestors, i.e. one with a pair of longitudinal ducts, and another 

 with a network of ducts. This would not perhaps be an un- 

 reasonable supposition were it not for the fact, that in this 

 case Lumbricus must have had a different origin from 

 Perichseta. The nature of this longitudinal duct has been 

 put in a fresh light by the observations of "Wilson (16) ; accord- 

 ing to this author it arises from the epiblast, and is therefore 

 comparable to the archinephric duct of Vertebrates, to which 

 the observations of several writers have concurred in assigning 

 an epiblastic origin. Haddon has recently (10) ingeniously 

 suggested how a continuous groove, into which the nephridia 

 opened, may have been converted into a canal opening into 

 the cloaca. But while in the Vertebrata it seems to be generally 

 agreed that the nephridial tubules are of mesoblastic origin, 1 

 Wilson states, that in Lumbricus they are budded out from 

 the longitudinal duct, and are therefore epiblastic, with the 

 exception of the funnel, which is mesoblastic. In any case his 

 investigations only relate to early stages; and there is therefore 

 nothing to negative the supposition that the portion which 

 arises from the longitudinal duct is the vesicular region of the 

 adult nephridium, which is known to be epiblastic, while the 

 rest is mesoblastic. 



Lang (11) dwells upon the identity of the longitudinal duct 

 of Annelids with the longitudinal canals of Platyhelminths, 

 but apparently in the belief that the former is of mesoblastic 

 origin like the latter. There are, however, now considerable 

 reasons for believing that the longitudinal duct of Lumbricus, 

 and possibly of Lanice, is epiblastic; this homology cannot 

 therefore be at present definitely accepted. 



In the meantime, therefore, I would submit (1) that the 

 origin of the Annelid excretory system from that of the 

 Platyhelminths is as has been suggested in the present paper, 

 (2) that the longitudinal duct of Lumbricus, La nice, &c, 

 has not any relation to that of the Platyhelminths. 



1 The pronephros has been described as formed by outgrowths of the archine- 

 phric duct, and therefore epiblastic. 



