164 STUDIES IN GENERAL PHYSIOLOGY 



The explanation is sometimes given that the tentacles of 

 Actinia are stretched by a contraction of the muscles of the 

 body- wall which forces water out of the body-cavity into the 

 hollow tentacles. The turgor of the tentacles of Cerianthus 

 cannot well be brought about in this way ; for, if this were 

 the case, the turgor of all the tentacles would have to be 

 decreased when the body-cavity is opened; but only the 

 turgor of the tentacles above the incision is diminished, 

 while it remains the same in the others. 



2. I amputated the heads of a large number of Ceri- 

 anthi. After some time which was, within certain limits, 

 shorter as the temperature of the water was higher new 

 tentacles were formed at the cut edge. I waited until the 

 newly sprouted tentacles had reached a length of 5 10mm. 

 when stretched out. I then made a partial transverse inci- 

 sion into the body and prevented the wound from healing 

 together. The tentacles above the incision lost some of their 

 turyor, and ceased to </)<>/< from that time on. The re- 

 maining tentacles, lio/rerer, continued to i/row and after 

 sereral irceks readied a lenyfh of 30 nun. or more when 

 stretched out. 



As I had to bring my experiments to a close, I could not 

 determine whether the wilted tentacles could again be made 

 to grow by restoring their turgor. I hope to be able to 

 make this and further experiments on growth at another 

 time. 



The fundamental condition for growth in plants is there- 

 fore also found in animals. 



XIV. ON THE EXTERNAL CONDITIONS WHICH DETERMINE THE 

 FORMATION OP TUBES IN CERIANTHUS MEMBRA NACEUS 



If a Cerianthus is laid upon the sand, and a sufficient 

 time is allowed the animal to burrow, it is noticed after 

 several days that the hole in which it lies is covered with a 



