240 



J. Stephenson : Two Oligoch^fe Worms. 



\"OL. I 



so that the whole chain was composed of six individuals or their 

 rudiments. As regards the posterior of the two chief components, 

 its anterior section was suificiently distinct, while a further subdivi- 

 sion in front of the sixth setal group, reckoned from behind, was 

 evidenced by the constriction and absence of nephridia at this 

 part. The corresponding subdivision in the anterior animal was 

 less evident owing to the non-development, up to that time, of 

 nephridia behind the level of the slight constriction. 



We can now, I think, summarize the history' of asexual repro- 

 duction in this species as follows : The normal single individual 

 consists of about eleven segments, but, in the spring of the year 

 at any rate, it is seldom found, and does not usually separate till 

 it has attained a greater length than this. It contains, typically, 

 two nephridia in the seventh and eighth segments ; it also shows 

 already a zone of budding behind the eighth segment; a nephridium, 

 if present in the tenth segment, will ultimately become the first 

 of a posterior animal. About eight segments are intercalated at 

 the zone of budding, the three anterior of which belong to the 

 anterior half, and the five posterior become the anterior five seg- 

 ments of the second animal ; the setse of the ninth original segment 

 become the second setal bundle, i.e., the setse of the sixth segment, 

 of the second animal. The posterior end of the whole animal 

 produces three new segments, whereby we now have twent3^-two 

 in all, eleven for each half. The animal, however, seldom divides 

 at this stage, the components remaining attached until at least 

 a part of the above cycle has been repeated in each of them. 



SetcB. — There are no dorsal setse. The ventral setoe are slender, 

 somewhat small compared with the size of the animal, slightly 



curved in an / shape, with two unequal prongs and a small nodu- 



lus {v. text-fig. 3 A). Those of the second segment are directed 



Fig. 3. A, ventral seta of C. pellucidus ; B, genital seta. 



