236 Herbert W. Rand 
If our second possibility shall be found to obtain—that 1s, if it 
shall be shown that the tentacle possesses no nervous mechanism 
of a kind adequate for an explanation of the distinctively different 
responses of proximal and distal cut ends, then a structural basis 
for these differences must be sought in the finer details of proto- 
plasmic structure which, with the means now at our command, 
are still beyond the reach of our senses. 
It is essential first of all that we gain full knowledge of the histo- 
logical conditions of the organism. The peculiar difficulties 
attending the study of the histology of the actinians, particularly 
that of the neuro-muscular mechanism, are such that the applica- 
tion of modern methods—see, for example, the work of Havet (’or) 
—has really advanced our knowledge of the finer details of their 
structure very little beyond the results of the classic researches of 
the Hertwigs (’79). If the behavior of the tentacle becomes 
intelligible on the basis of a nerve-muscle arrangement, then the 
polarity problem is merely transferred into ontogeny, where we 
again encounter it in undiminished importance. What deter- 
mines the origin of that structural polarity which later finds ex- 
pression in the constantly different behaviors of proximal and 
distal ends? If no such nerve-muscle arrangement is found, we 
must then search for some still more recondite protoplasmic 
mechanism which shall operate in such a way that identical causes 
—a cut surface— shall give rise to different kinds of effects in the 
two opposite directions of the length of the tentacle. A tentacle 
can bend in any direction, and when not specially stimulated it does 
so. But when it is stimulated by food it bends directly toward the 
mouth and in no other way. What is the mechanism at the bottom 
of this very useful behavior? We may well doubt if that final 
analysis of protoplasm which is implied in the answers to such 
questions as these is humanly possible. And so long as the dis- 
covery of protoplasmic mechanism appropriate to the final explana- 
tion of at least some one vital process remains unachieved, we 
cannot exclude from our minds the possible alternative—an alter- 
native so remote from our full conception that we may venture 
to state it only in the form of a question. May it be that a certain 
protoplasmic structure, no matter how simple or how complex, 
