FORM-REGULATION IN CERIANTHUS. 2O/ 



wall leaving the aboral end of the oesophagus free in the enteron 

 (Fig. 14). Such pieces do not differ essentially from pieces in 

 which the aboral end lies below the oesophageal region. They 

 become distended in the usual manner and regenerate typically, 

 but more rapidly than pieces in which regeneration of mouth and 

 oesophagus occurs. 



In the other case the cut surfaces of body-wall and oesophagus 

 unite in the manner described above (Fig. 8), either completely 

 or on a part of the circumference. Then it may happen that 

 different portions of this region of growing tissue are brought 

 into contact as in Fig. 12. The result is the union of all these 

 parts and so the closure of the aboral end (Fig. 13). The con- 

 nection between the oesophagus and body-wall is soon broken as 

 the piece becomes more fully distended and the condition repre- 

 sented in Fig. 14 is attained. From this stage on regeneration at 

 both ends proceeds in the typical manner. In some cases this clo- 

 sure of the aboral end and loss of connection between oesophagus 

 and body-wall does not occur at first, but later the margins of 

 the body-wall happen to come into contact perhaps in conse- 

 quence of the gradual decrease in distension mentioned above as 

 following the first increase, and thus closure occurs and is fol- 

 lowed by renewed distension and rapid regeneration. Appar- 

 ently the new tissue retains the power of making new unions for 

 a considerable time after the cut surfaces of body-wall and oesoph- 

 agus appear to be firmly united. 



The final result in all oesophageal pieces in which the aboral 

 end succeeds in closing aboral to the oesophagus is typical regu- 

 lation with well-developed tentacles at the oral end and several 

 millimeters of new tissue at the aboral end. 



The data of a few experiments will serve to indicate the uni- 

 formity of results. In all cases C. solitarius was used. 



Series jo. 



September 28, igo2. Seven oesophageal pieces were prepared 

 from large specimens in good condition as follows : at the oral 

 end of each animal a transverse cut was made through the disc 

 at such a level that the marginal tentacles and margins of the 

 disc were removed and the labial tentacles were cut off near their 



