290 MENSCH. [Vol. XVI. 



(PI. XIII, Fig. 13). In comparing it with a parapodium of 

 the Polybostricus, it will be noticed that, besides being smaller, 

 the dorsal ramus (d.r) has remained quite short, while the ven- 

 tral has pushed out some distance beyond it, thus carrying the 

 insertion of the short setae external to that of the swimming 

 setae and presenting a condition reverse to that of the male 

 parapodium. The insertion of the parapodium does not extend 

 as far dorsal as it does in male stolons, and hence the dorsal 

 contour of the stolon remains more like that of the parent 

 stock. As no further growth takes place after this stage of 

 development has been reached, such a parapodium presents all 

 the characteristics of a parapodium of a fully matured Sacco- 

 nereis. The sexual products appear very early, and even in 

 stolons no older than stolon i. Fig. 6, small ova are plainly 

 visible through the thin body-wall, and by the time the stolon 

 reaches a stage corresponding to that of stolon 6, it assumes a 

 darker color and becomes very much more opaque, due to the 

 accumulation of a large number of ova in the body cavity, the 

 outlines of which can be distinctly seen in a surface view. 



The separation of the female stolon takes place some time 

 before the formation of the egg-sac, and at the time when the 

 stolon breaks from the chain it is well distended with closely 

 packed ova which extend even into the cavities of the para- 

 podia, and the swimming setae have been fully developed. Such 

 specimens at once acquire the habits of the fully matured indi- 

 vidual and may be found swimming at the surface associated 

 with the fully matured individuals. Shortly after the libera- 

 tion of the stolon the ventral cuticle begins to become more 

 distended, and before long the ova begin to accumulate in the 

 ventral sac and the stolon presents the appearance of the 

 mature Sacconereis. 



Histological Phenomena of Stolonization. 



Internal Structures of the Mature Stolon. — Prior to taking 

 up the histological changes in the development of the young 

 stolons, I shall briefly describe such structures of the ma- 

 ture stolon as form the regions in which the most important 



