312 MENSCH. [Vol. XVI. 



stolon and also take part in the formation of the last seg- 

 ments that are added to the almost mature stolon, the forma- 

 tion of new segments in a region anterior to the anal segment 

 must be regarded as a secondary process and not the primary 

 factor in the elongation of the stolon ; and the Zooiiite forma- 

 tetir cannot in this species, at least, have the significance that 

 Malaquin attributes to it in the Syllidians in which he has 

 made these observations. 



Separation of the Stolon. 



As the young stolons of the chain become more differentiated, 

 it has been seen in the lateral and ventral views of the united 

 stolons that the region of the anal segment adjoining the head 

 parts of the succeeding stolon becomes somewhat distinct from 

 the anal segment in external appearance, and forms what I have 

 designated as the region of separation. In sections this region 

 forms in young stolons an indistinguishable part of the anal 

 segment, and even in older adjoining stolons, in which it is 

 externally visible as a distinct band, sections of this region 

 merely show a decrease in the amount of mesodermal tissue 

 ventrally and laterally (PI. XIV, Fig. 23, r.s), and a similar 

 decrease in the entire ectodermal tissue. (The ventral projec- 

 tion of the ectoderm in this section is due to abnormal contrac- 

 tions.) The tissues of this zone, however, do not remain as an 

 intrinsic part of the anal segment, but at a later stage are made 

 distinct by the appearance of a degenerative process in the ecto- 

 dermal cells, particularly in the ventral region (PL XIV, Figs. 

 26-28, r.s). This degeneration of the ectodermal tissue in the 

 ventral region also extends to the nerve cord, effects its sever- 

 ance, and at the same time so weakens the tissues in this place 

 that, by the independent movements of the stolon, separation 

 from the chain is readily accomplished. 



Claparede (4), de St. -Joseph (7), and Pruvot (8), in different 

 species of Syllidians have described the separation of the stolon 

 as taking place between two segments. In chain-bearing Syl- 

 lidians, like Autolytus varians, in the separation of its stolons 

 from the chain, it appears to me incorrect to make this state- 

 ment ; for, even if the zone of separation be regarded as an 



