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 5-10 mm. 

 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 

 turgor, and ceased to grow from that time on. The re- 

 maining tentacles, however, continued to grow and after 

 several weeks reached a length of 30mm. 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 OF 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 



