128 C. M. CHILD. 







PIECES REOPENED AT INTERVALS. 



In experiments of this kind the results are more or less modi- 

 fied by certain complicating factors which it is difficult to elimi- 

 nate completely. Some discussion of these is necessary before 

 proceeding to an account of the experiments. 



The region of the piece selected for opening was in most cases 

 the aboral end simply in order that the region subjected to the 

 irritation connected with repeated manipulation might be as far 

 removed as possible from the regenerating region. As a matter 

 of fact it was found that the manipulation itself, even though fre- 

 quently repeated and including extensive section or tearing of the 

 tissues, exerted little or no influence on the course of regenera- 

 tion in other regions of the piece. 



The description in the third paper of this series ('04^) of the 

 process of inrolling of the body-wall after section in consequence 

 of the elasticity of certain of its layers explains the necessity 

 for repeated opening of a piece when continued communication 

 between the enteron and the exterior is desired. In practice 

 it was found that within a half hour after section the open- 

 ing was usually reduced to mere slits and crevices by the ap- 

 proximation of its margins. Moreover, the ectodermal slime, 

 which plays an important part in the provisional closure of 

 wounds, as was described in the third paper ('04^), aids in plug- 

 ging the small spaces between the approximated margins. In 

 consequence of these two factors, the inrolling of the body-wall 

 about a cut and the presence of slime which plugs the crevices, 

 the attempt to keep the enteron in constant communication with 

 the exterior through an artificial opening meets with great diffi- 

 culties. The attempt was made to avoid these complicating con- 

 ditions by introducing a glass tube into the body through the 

 opening, but even when the tube was provided with a lip to hold 

 it in place the pieces succeeded in creeping away from it, and 

 when it was secured by a ligature the body separated at the liga- 

 ture if this was drawn tightly, or gradually drew itself out if the 

 ligature was loosely tied. All attempts to keep the end open by 

 the introduction of some foreign body failed. 



The only other possibility in pieces of such a form that closure 

 is possible is the repeated opening and spreading apart of the 



