152 C. M. CHILD. 



is sufficient to account for the fact that a spreading of the disc as 

 well as growth in the oral direction occurs. The disc is never 



o 



flat, but always somewhat funnel-shaped, indicating that the mar- 

 gins are the regions of most rapid growth. It is possible that 

 actual in vagi nation of the ectoderm at the center of the disc to 

 form the oesophagus does not occur, but that the surrounding 

 parts are pushed orally and peripherally by the internal pressure, 

 leaving this portion behind, as it were, since it is firmly attached 

 to the mesenterial margins. Goette ('98) states that the devel- 

 opment of the oesophagus in the young Cerianthns occurs in this 

 manner, though he does not express himself regarding causes. 



Although the above suggestions have been made in more or 

 less positive form, since that was more brief and convenient, I 

 desire to state once more that I am well aware of the hypothet- 

 ical character of many of them. That the general internal 

 water-pressure does play an important part in the regenera- 

 tion and reestablishment of the characteristic form in Cerian- 

 thns I believe the experiments already described have demon- 

 strated. As regards the details, however, and especially as 

 regards the effect of local pressure due to circulatory currents 

 extended experiment is necessary before final conclusions are 

 possible. These suggestions I have made in the hope that 

 they may aid both in making clear the interpretation which 

 seems to me possible and in pointing the way for future experi- 

 mentation. In later papers I shall bring forward additional evi- 

 dence upon the problem. 



SUMMARY. 



1. In pieces which are kept open or opened repeatedly at the 

 aboral end the appearance and growth of the tentacles, the 

 growth of the disc, and in fact all regenerative phenomena at the 

 oral end are delayed. The marginal tentacles which appear 

 under these conditions are short, blunt, and more or less sac-like 

 in form. Labial tentacles rarely appear at all until closure and 

 distension has occurred. 



2. In pieces cut in such manner that closure is prevented or 

 delayed retardation of regeneration occurs as in the cases just 

 mentioned. 



