64 C. M. CHILD. 



present in such pieces. The inrolling of pieces after section is 

 not then a definite reaction adapted to close the wound, except 

 in so far as we may regard the presence of an elastic layer in the 

 body-wall as an adaptation. 



After the inrolling is completed gradual reduction in the size of 

 the whole piece continues until the artificial openings are closed 

 by new tissue or otherwise and the water pressure is again estab- 

 lished in the enteron. This reduction in size can scarcely be due 

 to the loss of tissue in the absence of food, for that is much less 

 rapid. The piece appears to contract continuously after collapse 

 and closure and if the closure and distention with water is pre- 

 vented in any way, becomes much reduced within a few days. 

 Frequently new wrinkles or folds appear as the contraction pro- 

 gresses, indicating that it is not due to actual loss of material 

 but to some other cause. 



There can be no doubt that this reduction in size of collapsed 

 pieces is simply a continued reduction in the surface area of the 

 tissues resulting from mechanical conditions. It is due at least 

 in part to the elasticity of the body-wall (or especially of the 

 mesoglcea). This being effective in all directions must cause 

 gradual reduction in size of the whole after the inrolling of the 

 margins is completed, unless it is counterbalanced in some way, 

 which is not usually the case. This quality of the body-wall is 

 remarkable ; pieces kept under conditions where distention with 

 water is impossible often contract to half the size after section 

 and collapse. If they are then permitted to close and become 

 distended with water they may again attain in two to three days 

 almost the original size, provided the period during which they 

 remained contracted was not too long. The longer the period of 

 collapse the slower and less complete is the return to the 

 original size. These facts indicate that in the absence of the ten- 

 sion due to internal water-pressure the tissues gradually rearrange 

 themselves in accordance with the altered physical conditions. 

 There is no return to the " normal " form unless mechanical con- 

 ditions once more become normal. 



In his study of Ccriantlius, Loeb ('91) has attempted to explain 

 the collapse of tentacles and other phenomena by loss of turgor in 

 the cells. As I shall show in a later paper, this explanation is 



