HETEROMOKPHOSIS 151 



later. Fig. 32 shows the animal two months later. The cut 

 edges have coalesced, and the animal resembles somewhat a 

 normal Cerianthus. The inner row of small tentacles has 

 also been formed in addition to the large peripheral ones; 

 but and herein these phenomena again differ from those 

 observed in Hydra the number of tentacles is only a frac- 

 tion of the number of tentacles of the normal head, corre- 

 sponding to the size of the oral cut. Nor do the ends of 

 the two rows of tentacles meet to form a closed circle. 



After what has been said, it need not be emphasized that 

 the formation of tentacles is independent of food-supply, as 

 the taking up of food is impossible without a body-cavity. 

 When the pieces are too small, no tentacles whatsoever may 

 be formed. 



From all that has been said, the following observations 

 are easily understood. When a Cerianthus is cut completely 

 in two transversely, the aboral piece forms a new head, 

 bearing a normal number of tentacles, while at the lower end 

 of the oral piece, which has to regenerate a foot, new substance 

 is deposited upon the cut surface which restores the con- 

 tinuity of the ectoderm at this end and assumes the rounded 

 form of the foot. 



If head and foot are both cut from a Cerianthus, the 

 middle piece forms new tentacles at the oral and a new foot 

 at the aboral cut surface (the latter is formed more quickly 

 than the former). But this is possible only as long as the 

 pieces exceed a minimal size. 



5. I have tried to control the place where new tentacles 

 are formed by contact stimuli or by orienting the animal in 

 different ways against gravity and light. All of these experi- 

 ments have thus far been unsuccessful, if for no other rea- 

 son, because it was impossible to maintain the animal in any 

 abnormal position for any length of time. The following 

 chapter will give the reasons for this behavior. 



