422 NATURAE, SCIENCE. JUNE, 
many, the fact that there were eight of them would be difficult to explain, 
though, of course, it might be suggested that this was necessary to 
enable the animal to determine the direction in which the sound 
reached it; but, even then, the limited powers of locomotion would 
seem to render such a sense useless, and hence the evolution of the 
organs could not be explained by Natural Selection, nor yet, since the 
animal has no vocal organs, by sexual selection. 
Temperature may, perhaps, affect them, but if so surely it 
would affect all alike, and eight would not, therefore, be more useful 
than one or two; nor is their structure explicable on the hypothesis 
of sensitiveness to temperature. 
It may be well, therefore, to enquire what are the conditions 
under which the animal lives, and what are the dangers to which 
it is exposed. 
The danger from living enemies may be left out of account, for 
the abundant supply of thread-cells and the very small percentage of 
matter useful for food which they contain make them almost useless 
as food for other animals, and, even if it were not so, they have no 
means of escaping from any animal which might pursue them. 
These animals are pelagic, that is, they live in the open ocean, 
near its surface. The tissues of the body are so delicate that it is 
difficult to lift one from the water without tearing it to pieces. The 
dangers of the storm-tossed surface of the ocean for such an animal 
are, in part at least, obvious, but it is less obvious how they are 
avoided, especially if the animals be devoid of judgment and even of 
consciousness. The view I propose to offer is, that the tentaculocysts, 
without giving rise to sensation, serve to automatically steer the 
animal in such way as to keep it out of the way of its chief dangers 
and, at the same time, in the region where its food most abounds. 
How this is effected can only be made clear when we know some- 
thing about the nature of the disturbance which we call a wave. 
It is not easy to know very much about a wave without also 
knowing more about certain branches of higher mathematics than is 
usual among zoologists. Parenthetically, I may, as a biologist, admit 
that the Senior Wrangler who defined a biologist as ‘‘a man who 
cannot solve a mathematical problem,” came sufficiently near the 
truth to make the epigram a distinctly unpleasant one! 
Those biologists who are undismayed by formidable formule, 
and who have not as yet studied wave-movements of water from the 
mathematical point of view, will find the greater part of the problem 
treated mathematically by Lamb (1) and Basset (2); but I wiil 
assume that the Senior Wrangler was right, and that the biologist is 
a man of observation rather than of mathematical investigation, and 
I will, therefore, appeal rather to his power of observing than to his 
mathematical faculty. 
It is unfortunate that at times in our dredging excursions, when 
the waves are largest and best fitted for study, those of us who lean 
