Regeneration in Polychcerus Caudatus. 339 



removed. Figs, R and S show the result in two cases of diagonal 

 section, as in Fig. A, — p, and r — x, after four weeks. In Fig. R 

 the posterior end on the regenerating side is in approximately the 

 same condition as in cases of entire posterior regeneration. In 

 Fig. S, an abnormal notch and appendage has developed near j, 

 as though the notch and appendage were a necessary accompani- 

 ment of posterior regeneration without regard to the presence of 

 the same structure in the old part. This phenomenon also recalls 

 the supplementary heads and tails described by Morgan ('01) and 

 others, as appearing on long obliquely or longitud.nally cut 

 surfaces. 



General Discussion. 



The results of the experiments show that in Polychcerus cauda- 

 tus anterior regeneration at different levels may proceed much as 

 in many fresh-water forms (Figs. G, M and P), or it may be pre- 

 vented or delayed, not by muscular contraction and union of the 

 muscle bands, as described by Schultz ('02), but by a folding 

 under and union of the cut edges. (Fig. F, e — f.) That such 

 union of the cut edges is not an insuperable h'ndrance to regenera- 

 tion in this form is proved by such cases as are shown in Figs. F, 

 L and O, where regeneration begins with the formation of a V of 

 new tissue and ends with the production of a typical head- 

 region. 



In Polychcerus there is no axial gut (Bardeen, '01), nor is there 

 a central nervous system to influence regeneration (Lillie, '00; 

 Child, '04). The fact that head-pieces, which are more active, 

 regenerate more rapidly than middle-pieces or tail-pieces, might 

 be held to support Child's theory that "there is a close parallelism 

 between the rapidity, amount and completeness of regeneration 

 and the characteristic activity of the part concerned;" but the 

 difference in rate of regeneration and morphallaxis is not propor- 

 tionate to the difference in activity, for head-pieces are easily 

 stimulated into activity by changing the water or jarring the dish, 

 while middle-pieces and tail-pieces hardly move at all during the 

 first two weeks unless violently disturbed. The difference in 

 activity is great, while the difference in rate of regeneration is 

 comparatively small. 



So far as regeneration in Polychcerus has been tested by these 

 experiments, it seems to be largely a question of "organization" 



