212 C. M. CHILD. 



oesophagus and that of the body -wall may also play a part in 

 the result. Whatever be the cause, the result is free communi- 

 cation between a fully formed oesophagus and the small enteric 

 cavity with its intermesenterial divisions. If entrance of water 

 through the oesophagus serves to maintain internal pressure in 

 Cerianthns it is clear that in these pieces the pressure should at 

 once become about equal to the pressure in a normal animal 

 since the mouth opening and oesophagus are not regenerated 

 structures but parts of the parent body and of full size. If 

 internal water pressure affects regeneration we might expect in 

 these pieces rapid regeneration, even more rapid than in pieces 

 with regenerating mouth and oesophagus. Close comparison of 

 these pieces with others in which mouth and oesophagus are 

 formed by regeneration is difficult, since in the cesophageal 

 pieces regeneration may be at first delayed until the aboral 

 closure is complete, but the piece in Series 30 in which closure 

 of the aboral end occurred between October 4 and October 7 

 and by October 15 the marginal tentacles were S-io mm. and 

 the labial tentacles 5-6 mm., show the rapidity of regeneration. 

 In fact regeneration in this piece after closure is more rapid than 

 in any other case noted in my records with the exception of 

 other pieces of the same kind. 



The striking difference between cesophageal pieces in which 

 the aboral closure occurs and those in which it does not consti- 

 tutes evidence of great importance for the influence of internal 

 water-pressure on regeneration. As regards the influence of 

 local pressure due to circulatory currents in determining the posi- 

 tion of tentacles and in their regeneration these experiments afford 

 no direct evidence. They show merely that the greater the dis- 

 tension of the piece and consequently the more widely open the 

 intermesenterial chambers and the greater the force and volume 

 of the circulatory currents the more rapid is regeneration. 



SUMMARY. 



i . In pieces with oblique oral end the rapidity of tentacle re- 

 generation differs on different parts of the disc, being greatest on 

 the uppermost (most oral) portion and least on the lowest (most 

 aboral) portion. The delay in regeneration on the lowest portion 



