2IO C. M. CHILD. 



pieces regeneration has proceeded in the typical manner ; mar- 

 ginal tentacles 56 mm.; labial tentacles 23 mm. 



In the other two pieces regeneration has proceeded no further. 

 They are still only slightly distended and with minute tentacle- 

 buds. 



In this series a larger proportion of the pieces closed aborally 

 across the end of the oesophagus than in any other series of this 

 kind. The date of this series was later in the year than that of 

 any other, /. e., the temperature of the water was lower and the 

 distension of the pieces occurred much more slowly (see Child, 

 '03$). It is probable that different parts of the aboral cut sur- 

 faces of the body-wall remained in contact for a longer time than 

 in the other cases where distension occurred more rapidly, and 

 that this prolonged contact made union possible in a greater 

 number of cases than in other series. Other conditions such as 

 difference in the degree of contraction of body-wall and oesoph- 

 agus at the time the lower cut was made may have aided in 

 bringing about this difference. However that may be, the point 

 of chief importance, viz., the difference in regeneration between 

 those pieces which did close aborally across the oesophagus and 

 those which did not is as clear in this series as in others. 



While the general result of these experiments is sufficiently 

 clear special attention may be called to certain points. 



In all cases in which the oesophagus remains open aborally 

 and consequently does not communicate with the enteron the 

 pieces never become fully distended and regeneration is slight. 

 Pieces cut below the cesophageal region become well distended 

 and the marginal tentacles may attain a length of 23 mm. be- 

 fore the mouth is formed. In my first paper ('03^) diffusion of 

 water through the body-wall in consequence of the presence of 

 soluble products of metabolism or other substances in the en- 

 teron was suggested as a possible cause of this first distension. 

 It is also possible that secretion of fluid into the enteron occurs. 

 In the cesophageal region the entodermal layer is thinner and 

 undoubtedly of less functional importance than in the region 

 aboral to the oesophagus, and it is reasonable to suppose that the 

 accumulation of fluid in the cesophageal pieces would be much 

 less rapid than in pieces from regions aboral to it. If this be 



