34 



C. M. CHILD. 



ends ; piece somewhat distended with water ; marginal tentacles 

 just beginning to appear, about i mm. in length; no labial ten- 

 tacles (Fig. 4). 



II. Body-wall and oesophagus united orally so that a mouth 

 is formed. Aborally the cut end of the body-wall is closed. 

 The oesophagus therefore opens into the enteron. The piece is 

 distended and the marginal tentacles are 2 mm. in length. No 

 labial tentacles (Fig. 5). 



September g. — I. Piece slightly distended ; marginal tentacles 

 barely visible ; no labial tentacles. 



II. Fully distended ; marginal tentacles 5-7 mm. in length ; 

 labial tentacles just visible. 



a 



.b 



- c 



3 



September 18. — I. Collapsed ; neither marginal nor labial ten- 

 tacles visible. 



II. Fully distended ; marginal tentacles 8-10 mm. in length ; 

 labial tentacles 1-2 mm. 



October 8. — I. Collapsed ; much reduced in size and body- 

 wall undergoing atrophy. No traces of tentacles. 



II. In burrow, distended; marginal tentacles 18-20 mm.; 

 labial tentacles 4-5 mm. 



Later History. — I. After October 8 complete atrophy of the 

 body-wall along the line of folds occurred and the piece broke 

 up into fragments which continued to decrease in size and undergo 

 atrophy until they died. 



II. Remained in good condition in burrow until December 3 i 

 when experiment concluded. Marginal tentacles 20-25 mm. in 

 length ; labial tentacles 5 mm. 



The difference in the process of regulation between these two 

 pieces is very great. In piece I. the development of marginal 



