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 
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 MEMBRANACEUS 
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 
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