NOTES ON REGENERATION. 169 



kept about twenty-four hours when the primoidia of the new 

 tentacles had begun to appear. At this time I cut the ends 

 squarely off, the plane of section lying across the middle of the 

 new proximal tentacles. To my surprise the cut ends now 

 closed in a very different way from that of ordinary cross-cut 

 pieces. The whole wall contracted from the perisarc and the 

 cut edges were brought together almost at once, and subse- 

 quently fused, often showing the radiating lines described by 

 Stevens over the new end. It was perfectly clear that the result 

 was due to a contraction of the ccenosarc, and the difference be- 

 tween this process and that shown by ordinary pieces appears to 

 be due entirely to the fact that at the time when the tentacle 

 primoidia are laid down, the ccenosarc has become free from the 

 outer wall, or perisarc. 



From this result it seems to me to follow with great proba- 

 bility that in ordinary pieces the closure of a cut end is also due 

 to a process of contraction of the ccenosarc, but ordinarily the 

 wall of the ccenosarc is so closely stuck to the inner surface of 

 the perisare that it is not free to pull away as a whole, and 

 there is a consequent drag that holds back the contracting wall, 

 and a consequent modification of the method of closure of the 

 opening. This conclusion also fits in well with some facts ob- 

 served at the time of closure of the pieces. Certain of the cells 

 that appear to be more closely stuck to the wall are often left 

 behind, or are retarded in their progress towards the center of 

 the newly forming membrane. Thus the peculiar method of 

 closure of Tnbularia finds its explanation in the unusually close 

 connection between the perisarc and ccenosarc. I have tried to 

 show elsewhere * that this same connection may also be respon- 

 sible for the characteristic " incomplete structures " of Tubidaria, 

 whose chief peculiarity is that their organs are full sized so far as 

 they are formed. 



TRANSPOSITIONAL OR COMPENSATORY REGENERATION OF THE 



LARGE CHEL/E IN SOME CRUSTACEA. 



Przibram 2 discovered in 1901 in the decapod Alplieus that it is 

 possible to cause the small claw (chela) of one side to become 



1 " Some Factors in the Regeneration of Tubularia," Roux'' 's Archiv, XIV., 1903. 

 2 J?oux's Archiv, XL, 1901. 



