REGULATION OF HARENACTIS ATTENUATA. 



49 



In Harenactis, as in Cerianthus, the healing of the wound made 

 by a lateral incision in the cesophageal region and deep enough 

 to involve the oesophagus occurs in the manner indicated in Fig. 

 2. The cut surfaces of the body-wall and the cesophagus unite 

 with each other both distal and proximal to the cut so that a 

 new lateral opening into the oesophagus 

 is formed, its extent depending on the ex- 

 tent of the incision. The factors concerned 

 in this method of closure will be discussed 

 elsewhere : at present we are concerned 

 merely with the fact of closure in this 

 manner. After healing of the wound ten- 

 tacles appear proximal to the opening, i. e., 

 on the distal end of the region below the 

 opening, their number depending on the 

 number of inter-mesenterial chambers 

 which were cut across by the incision. So 

 far Harenactis and Cerianthns are alike. 

 In Harenactis, however, but not in Ceri- 

 anthus, heteromorphic tentacles appear 

 somewhat later at the proximal end of the region distal to the 

 cut (Figs. 3 and 5). As will be shown elsewhere heteromorphic 

 tentacles appear much more readily in Harenactis than in Ceri- 

 anthns under various conditions. After these lateral incisions in 

 the cesophageal region they always appear. If the old disc is 

 removed at the time the lateral incision is made tentacles de- 

 velop about the whole circumference of the distal end of the 

 body. My figures represent cases in which the original disc was 

 left intact : the final result is the same whether the old disc is 

 removed or not. 



After an operation of this kind in Harenactis there exists then a 

 region distal to the lateral opening in which the inter-mesenterial 

 chambers are completely shut off from other portions of the en- 

 teric cavity in the longitudinal direction. The presence or ab- 

 sence of communication in the transverse direction, however, de- 

 pends on the position of the incision : if this was made distal to the 

 ostia(#, Fig. i) each chamber is completely isolated from the others 

 and from other portions of the enteron ; if, on the other hand, 



FIG. 2. 



