2/6 C. M. CHILD. 



in morphogenesis but to afford little basis for other interpreta- 

 tions. I desire to give the data in descriptive form, but shall 

 endeavor to point out their bearing in connection with this hy- 

 pothesis. It should be borne in mind, however, that while the 

 existence of a general relation between internal water-pressure 

 and growth is demonstrated, my data upon the other problem 

 are insufficient in my own opinion to establish a conclusion with- 

 out doubt. At present, though the evidence in regard to the 

 marginal tentacles is very strong, the impossibility of giving any 

 special evidence concerning the labial tentacles constitutes a ser- 

 ious defect. The regeneration of labial tentacles is certainly 

 delayed or inhibited by reduced water-pressure, but I have not 

 been able thus far to demonstrate that localized pressure upon 

 the body-wall occurs in the region where they appear. This 

 failure is due at least in part to the fact that my attention was 

 concentrated chiefly on the marginal tentacles during my experi- 

 ments. I hope that a future opportunity for renewed experi- 

 mentation may render it possible to attain more definite conclu- 

 sions on this point. Attention may be called to the possibility 

 that the two sets of tentacles possessing different functions and 

 appearing as they do at different times and under different con- 

 ditions may perhaps be determined by very different factors. 

 General similarity f form and structure is not necessarily indic- 

 ative of similar conditions of origin. Even if it should be demon- 

 strated that the marginal tentacles arise in response to the stimu- 

 lus of localized pressure it would by no means necessarily follow 

 that the labial tentacles are similarly produced. 



THE CLOSURE AND DISTENSION OF PIECES. 



The closure by new tissue of the two ends of cylindrical pieces 

 has been described in the first paper of this series (Child, 'c>3<?). 

 The closure consists essentially in typical cases of the connection 

 of all parts of the inrolled cut surface of the body-wall by a thin, 

 delicate membrane of new tissue. The result of closure in this 

 manner of both ends of the piece is the interruption of direct 

 communication between the enteric cavity and the exterior. 

 Nevertheless, water rapidly accummulates within the enteron, 

 probably in consequence of diffusion or secretion, causing marked 



