Wound Reparation—Actinian Tentacles 211 
this conclusion. In the first place, the closing reaction may fol- 
low the cutting almost instantaneously. ‘There is, indeed, con- 
siderable variation in the promptness of the reaction depending 
mainly upon the level at which the tentacle is cut. It is when the 
transection is located at the tip of the tentacle that the reaction is 
most prompt. Here the closing takes place so quickly that the 
internal pressure is released only for an instant. The tentacle 
does not have time to collapse. A cut at the extreme tip often 
causes comparatively little contraction of the tissues of the ten- 
tacle—particularly in Aiptasia. ‘Therefore the original conditions 
of extension and internal pressure are restored immediately after 
the cutting, or, in fact, they are scarcely interrupted by the cut- 
ting. But when the transection is nearer the base, then there is 
much contraction of the stump of the tentacle and several minutes 
may elapse before its cut end is closed. However, during the 
period of contraction the closing of the end makes comparatively 
slow progress, although a gradual narrowing of the opening does 
take place beginning immediately after the cut is made. But 
when the tentacle begins to extend, the cut end closes in very 
quickly and with continued extension the nipple is formed. Thus 
the closing appears, for the most part, to await the extension of the 
tentacle and then takes place within a few seconds. In all cases, 
then, there is to be seen a rapidity of closing which is inconsistent 
with the view that the process depends upon amceboid motion or 
that it is of the nature of growth changes. In view of the known 
histological structure of these tentacles it can hardly be questioned 
that this rapid closing of the cut end is due to contraction of circu- 
lar muscle fibers. 
In the second place, the appearance of the tissues in the nipple 
and around the base of it is such as may be seen in any contracted 
part of an uninjured normal tentacle. ‘The tentacle wall in exten- 
sion is yellowish and translucent. When contracted it is whitish 
and opaque, and the more it is contracted the greater is the degree 
of whitishness and opacity. The white opaque nipple indicates 
extreme contraction of tissues. Passing proximad over the surface 
of the end of the tentacle the whitishness and opacity gradually 
diminish, merging into yellowishness and translucency just where 
