HETEROMORPHOSIS 163 



are stretched. This stretching of the cell membrane permits 

 the deposition of new material in the cell growth. When 

 the hydrostatic pressure in the cells of an organ attains a 

 height in which the cell membrane is tensely stretched, the 

 organ is said to be turgescent. 



In the course of the experiments detailed in the preced- 

 ing chapter I accidentally discovered a means by which the 

 turgor of a part of the tentacles of a Cerianthus can be 

 diminished, while in the others it remains unaltered. I used 

 this method to determine whether a diminution in the turgor 

 would decrease or stop the growth in animal organs. If a 

 transverse incision is made into the body of a Cerianthus 

 such as is necessary to cause the growth of a second head, 

 the incision has a striking effect upon the behavior of the 

 tentacles. If one watches such an animal when its tentacles 

 are stretched out, it is seen that those tentacles which are 

 situated above the incision are distinctly, often as much as 

 one-half, thinner and shorter than the remaining tentacles. 

 This difference is shown distinctly in Fig. 29 which repre- 

 sents the same animal as Fig. 28, only viewed from another 

 side. This difference in the turgor of the tentacles is per- 

 manent when the incision is made near the oral plate, and 

 when the edges of the wound are not allowed to heal to- 

 gether. As soon as the wound heals, the turgor of the 

 tentacles is re-established. If the irritability of such wilted 

 tentacles is compared to the irritability of the turgescent 

 tentacles of the same animal, it is found that the irritability 

 is not markedly changed during the first few days after 

 the incision. 



If a piece of meat be carefully laid upon the tip of such 

 a wilted tentacle, it is carried to the mouth in the same way 

 as by an erect tentacle. Only it seemed to me that the 

 movement of the wilted tentacle was slower and more awk- 

 ward than that of the turgescent tentacle. 



