28o MENSCH. [Vol. XVI. 



the first setigerous segment and its forward extension slightly 

 beyond the anterior region of this segment. The forward exten- 

 sion of this new tissue is confined in greater part to the dorsal 

 surface and has the appearance of a thickened plate, with the 

 lateral portions bulging out so as to give the appearance of the 

 two lateral lobes. At the sides this plate tapers into a narrow 

 rim which is lost in the lower lateral margin of the segment on 

 a plane with the parapodia. This stage of development has 

 been reached by a gradual elevation and forward extension of 

 mostly the anterior part of the first setigerous segment. The 

 very first indication of this growth is a slight thickening of 

 almost the whole dorsal wall of the segment, which gradually 

 becomes more marked anteriorly and soon forms a prominent 

 ridge over the anterior dorsal and lateral portions of the seg- 

 ment. Subsequently this ridge begins to bulge forward in the 

 form of a prominent rim, with two faint lobes laterally, beyond 

 which it gradually becomes less marked until near the ventral 

 surface, where it disappears. 



Stolon I, therefore, presents two regions of growth. The 

 one anterior to and including the anal segment which, as I 

 have already indicated in the description of the preceding 

 stolon, is rapidly contributing to the increase of the number 

 of setigerous segments. The other is a new region, which has 

 appeared prominently for the first time in this stolon. This 

 new region is developed secondarily in a segment which has 

 originally been separated from the parent stock, and appears 

 shortly after the region of growth anterior to the anal segment 

 has become active. Thus the different structures of this stolon 

 have originated in three ways : (i) from segments derived di- 

 rectly from the parent stock ; (2) from segments derived from 

 the anal region of growth ; (3) from outgrowth from the ante- 

 rior segment of the series. Of these, the last two contribute 

 to the future development of the stolon. 



Stolon 2 represents a stage a little more advanced than 

 stolon I, and presents the most important changes which next 

 take place in the process of development. It consists of fifteen 

 setigerous segments, the anterior ones of which are consider- 

 ably larger than those of stolon i, while the more posterior com- 



