ON CH^TOBRANCHUS. 87 



The nephridia are not very clearly seen, but are undoubtedly 

 present, a pair in each of the segments. In the middle region 

 of the body they have exactly the same appearance as have the 

 nephridia of Naids. 



Asexual Reproduction. — Although I have examined a 

 very large number of individuals I have found a few specimens 

 only in the act of asexual reproduction, and this process 

 appears to be more like one of simple fission, as opposed to 

 gemmation, than it is in Naids and Chaetogaster. In these 

 latter forms a new region, a " budding zone," is produced 

 between two existing segments ; this divides into two portions : 

 the anterior portion forms the new tail of the anterior daughter 

 zooid, and the posterior portion forms a head for the posterior 

 daughter zooid, while the previously existing segments i of the 

 parent zooid undergo little or no change. 



InChsetobrauchus I cannot find any ''budding zone.^^ In 

 the specimen which is drawn in fig. 10, for instance, I counted 

 over 200 segments. The most anterior sixty segments bear 

 recognisable branchial processes, which, as usual, get smaller 

 as one passes backwards ; then there are about thirty segments 

 which bear no trace of processes ; then about forty-five seg- 

 ments on which branchial processes can be counted, the anterior 

 ones almost as large as those usually found in the head region, 

 and the posterior ones becoming so small as to be unrecognis- 

 able j behind the last process-bearing segment I counted about 

 sixty-five segments, the posterior ones very much crowded 

 together, as though active growth were taking place in this 

 region. 



This individual would doubtless soon have divided into two 

 zooids, the posterior one of which must form a head, consisting, 

 at any rate, of a buccal segment and a prostomium. The re- 

 markable feature in this process is the new growth which occurs 

 in connection with so many segments of the parent zooid, viz. 

 the development of the branchial processes in all those seg- 

 ments which bear them, and which subsequently form part of 

 the posterior daughter zooid. 



' Semper, * Arb. Zool. Zoot. Institut, Wurzburg,' Bd. iv, 1877-8. 



