234 



J. Stephenson : Tuw OHgochaste Worms. [Vol. I, 



Segmentation. — The prostomium is large, broad and some- 

 what shield-shaped {v. pi. viii, fig. i). It is broader than the 

 following segments, and is ciliated at its rim and on its ventral 

 surface. No ciliated pits were seen, but ciliary action appeared 

 sometimes to be especially well marked in two grooves leading 

 to the angles of the mouth ; possibly the grooves were not per- 

 manent. The smallest number of serial setal bundles met with 

 in a complete animal was ten ; and animals showing a larger num- 

 ber than this showed also, both by the arrangement of the bundles 

 and by commencing constrictions, that they were preparing to 

 divide (y. diagrams in text-fig. i). The normal number of seg- 

 ments for a single individual is thus probably about eleven. 





'-^v;'^r74^w=^^^44^- 



W\VvV 



x^vaI^ 



Fig. 1. — Diagrams illustrating various phases of asexual reproduction in ^■Eolosoma sp. 



Asexual multiplication. — Diagrams illustrating various phases 

 are shown in text-fig. i. It will be seen that the anterior, or origi- 

 nal, animal of the chain bears eight, nine, ten or eleven serial 

 setal bundles ; but of these the last, or the last two or three, are 

 evidently (as is indicated in the diagrams) of new formation. The 

 zone of budding, therefore, seems to arise after the seventh or 

 perhaps sometimes the eighth setal bundle, i.e., after the eighth 

 or ninth segment ; and the intercalation of two or of three seg- 

 ments in this place and subsequent fission would give us the 

 " normal " individual of eleven segments referred to above. In 

 the hinder part of the chain the division into individuals seems 

 to be much more irregular ; thus in text-fig. i / we appear to have 

 had the establishment of three zones of budding behind each of 

 three originally successive segments. 



SetcB. — Both dorsal and ventral setae are of the same type, — 

 long, smooth, straight, hair-like ; in both dorsal and ventral bun- 

 dles, however, shorter setae may be present, sometimes alternating 

 with the longer ones in their position in the bundle ; but though 



