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. Iused 
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. 
Digitized by Microsoft® 
