^^S N. M. Stevens and A. M. Boring. 



notch. Posterior regeneration in head-pieces (Figs. B and C) 

 follows more nearly the embryonic method of tail development 

 than does that of middle-pieces, where regeneration from the 

 beginning seems to be based on the adult form of the tail-region 

 which has been removed. 



Anterior regeneration varied greatly in different lots of material 

 and in different pieces of the same series. There are, however, 

 two distinct types. In most cases the cut anterior end, a — b, 

 folded together ventrally and the portions on either side of the 

 median line united as shown in Fig. F, e — /. In the first set of 

 pieces no anterior regeneration occurred while the material was 

 under observation. In another set, in which all the pieces regen- 

 erated better, a few at the end of two weeks showed a V of new 

 tissue between the united cut edges. Fig. F, g — e — h. At the end 

 of four weeks such pieces had developed as in Fig. L, g — e — h, 

 and later some of them produced typical worms. As the union of 

 the cut edges, as in Fig. F, e — /, appeared to hinder regeneration 

 in many cases, an attempt was made to prevent the union of the 

 edges or to remove the hindrance later on. Pieces were cut as in 

 Fig. A, X — y, or with a sharper angle, but the cut edges still curled 

 under and united as before. Cutting the line of union was 

 equally unsuccessful. There were a few pieces which contracted 

 at the anterior end without folding under and uniting; these 

 regenerated as shown in Figs. G and M, and in due time produced 

 worms of typical form. Anterior regeneration was, however, in 

 all cases less rapid than posterior. One piece produced a hetero- 

 morphic tail, Fig. H. This individual did not crawl normally, 

 but half crawled, half swam with great difficulty on its back or 

 side. This was the only case of heteromorphosis observed. 



Tail-pieces. 



Anterior regeneration of tail-pieces was of the two general types 

 described for middle-pieces and illustrated in Figs. O and P. 

 In general it was less rapid and less complete than in middle- 

 pieces. 



Lateral Regeneration. 



A few worms were cut longitudinally in various ways. Regen- 

 eration occurred along the whole cut surface as in other forms, the 

 new material being distributed in proportion to the amount 



