DYNAMICS OF REGENERATIVE PROCESSES 



209 



sary for their growth. In one experiment the oral disk of a Cerianthus 

 was cut off ; very soon new tentacles began to grow at the top, and 

 after having reached a certain size, an incision was made in the animal 

 at d, Fig. 47. The tentacles above the incision between b and c, Fig. 

 47, collapsed in consequence and ceased to grow, while growth of the 

 others between a and b continued. On the lower edge of the incision 

 new tentacles began to grow. 



Child* has elucidated to some extent these phenomena of turgidity. 

 Every tentacle is a hollow cylinder, and this cylinder continues down- 

 ward where it communicates with the body cavity. When liquid is 

 pressed into the tube from the body cavity, the tentacles are stretched ; 

 but if the liquid leaves the tube, the tentacles relax also. If an incision 

 is made below a tentacle into the wall of the body of a Cerianthus, no 

 more liquid can be pressed into that tentacle, and it relaxes. Child con- 

 firmed my observation, that regeneration of the tentacles in Cerianthus is 

 no longer possible when they relax. He added a number of pretty 

 demonstrations of the necessity of the 

 turgidity of the tentacles for regeneration. 

 He found, for instance, that if an incision 

 is made into the foot of a Cerianthus and 

 the edges of the wound are prevented 

 from healing together the tentacles lose 

 their turgidity and are no longer able 

 to grow. He found, also, that the ten- 

 tacles degenerate under such conditions. 



It is unknown at present how the 

 turgidity can influence growth in the 

 tentacles of an Actinian. 



The observations on Cerianthus are 

 comparable with those on Tubularia if 

 we realize that the body wall in Cerianthus 

 consists of a series of hollow cylinders or 

 spaces each of which ends in a tentacle. 



The idea of an animal body consisting 

 of a series of comparatively independent 

 longitudinal elements recommends itself 

 also for the understanding of a phenom- 

 enon of regeneration in Ascidians. The 

 Ascidian, Ciona intestinalis, has eyes 

 (ocelli) at the oral as well as at the aboral opening of the body (Fig. 

 48). We may imagine that each ocellus is the end of one of the 



* Child, Biological Bulletin, 1903-1904. 



FIG. 48. 



An incision was made at c and new 

 ocelli develop at both ends of the 

 cut. 



