216 Herbert W. Rand 
This difference in time is consistent with the difference in the 
cross sections of the two structures. The diameter of the tentacle 
in Condylactis is, in rough terms, from fifteen to twenty-five times 
as great as that of the trunk of Hydra viridis. In both cases the 
cut end becomes closed by old tissue; there is no proliferation of 
new tissue. In the introduction to this paper I have maintained 
that the closing in Hydra is dependent upon cell activities akin 
to amceboid motion. The structural closing of the distal cut end 
of an actinian tentacle is certainly due to some rearrangement of 
the tissue elements and any such rearrangement, necessarily 
involving changes in the form and relative position of cells, must 
depend upon cell activities closely allied to amoeboid motion. In 
so far, therefore, the processes of closure of the very simple stem 
of Tubularia, the more complex trunk of Hydra, and the still 
more complex and enormously larger tentacle of Condylactis 
are probably reducible to the same terms—changes in the form 
and position of preéxisting tissue elements. But in the total 
reaction of the large actinian tentacle there is to be seen one feature 
which is not exhibited by the tubularian stem or by Hydra, namely, 
the immediate but temporary muscular closing of the cut end. In 
this feature of the reaction is afforded a very effective muscular 
control of the cut distal end pending the completion of the slow 
process of structural repair. 
It seems reasonable to suppose that there is some advantage 
to the organism in the prompt closing of the injured end of a 
tentacle. The loss of a single one of the many tentacles possessed 
by these actinians cannot be a serious matter. But if a single cut 
tentacle were allowed to remain freely open it would not be long 
before the escape of gastro-vascular fluid and the release of the 
normal internal pressure must lead to a more or less serious dis- 
turbance of the entire organism. The prompt muscular closing 
of the cut has the result, very important to the organism, of obviat- 
ing this general disturbance or at least reducing it to a minimum, 
while—doubtless a much smaller advantage—the injured tentacle 
itself is almost immediately restored to a condition which, so far as 
its general reactions are concerned, appears physiologically normal, 
although no structural repair of the injury has yet been made. 
