Wound Reparation—A ctinian Tentacles 235 
or fibers. Even if it were a contraction of other than specialized 
muscles, it is nevertheless an expression of the contractility of pro- 
toplasm, which for our present purpose amounts to the same thing. 
As regards the action of these contractile elements, there are two 
possibilities; they may either be subject to the control of a nervous 
mechanism, or they may be entirely independent of specialized 
nervous structures. 
If the first one of these two possibilities obtains, then it may be 
observed that the very definite responses of the tissues situated 
upon the two opposite sides of a plane of transection imply an 
equally definite nervous arrangement. We may suppose, for 
example, that the contractile elements are associated with nerve 
fibers which extend only distad. In such a case, at least so far as 
the neuro-muscular mechanisin is concerned, transection would 
be followed by contraction upon the proximal side of the plane 
of cutting, but not on the distal side. It must be kept in mind that 
we are now concerned with the contraction of circular fibers only. 
Contraction of longitudinal fibers appears to play no part in the 
differences of behavior which characterize proximal and distal 
ends. Yet in the responses to tactile stimulation we see a simi- 
larity to the responses to transection in that, with moderate stimu- 
lation, longitudinal contraction takes place only on the proximal 
side of the point of stimulation. Further, this arrangement would 
seem to necessitate that the nerve fibers be short—perhaps not 
longer.than the length of the nipple. Otherwise, why should 
cutting cause maximum contraction of only that narrow band of 
tissue which forms the nipple and not of the tissue proximal to the 
nipple? ‘The partial contraction of the tissues proximad of the 
nipple, as a result of which the fragment of tentacle assumes a 
conical form, may be a secondary contraction conditioned by the 
extreme contraction at the distal end and not dependent upon stim- 
ulation directly from the cut surface. Or, if we suppose that the 
contractile elements are innervated indifferently from both prox- 
imal and distal directions, then we may imagine that the stimulus 
of a cut surface is transmitted only proximad, not distad; or else 
that there is contractile response only to a stimulus from the distal 
direction—that something inhibits contraction in response to any 
impulse proceeding from a proximal direction. 
