270 
ME. Gr. J. EOMANES ON THE LOCOMOTOE SYSTEM OF MEDUSAE. 
have already traced in all its details, as here described, in the genera Hippocrene ( Bou - 
gainvillia), Tiaropsis, and StauropJiora ” *. 
As my own observations on the histology of the Medusse are not yet complete, I do 
not intend to publish them on the present occasion ; but I may nevertheless be permitted 
to remark, with reference to the passage just quoted, that the conclusion so positively 
enunciated concerning the function of the structures described has always appeared to 
me, as it has appeared to biologists in general, a conclusion that is certainly unwarranted 
by the facts. As the learned Professor himself insists, the cells to which he so confi- 
dently attributes a nervous character represent “ a peculiar type of the nervous system, 
a type different from all those types which have yet been recognized in the animal 
kingdom ; ” and this fact alone, one would think, ought to have inspired extreme 
caution in founding deductions upon such a basis regarding a question of such high 
importance as is that concerning the presence of a nervous system in the class Plydrozoa. 
Whatever effect, therefore, the present paper may have in deciding this question, or in 
confirming the deductions of Prof. Agassiz, I wish to state, as emphatically as I can, that 
in my opinion these deductions were decidedly premature, and that hitherto the only 
legitimate attitude of mind to adopt towards the much-vexed question as to the presence 
of nerves in Medusae, is that which is thus tersely formulated by one of the greatest 
living authorities upon the group: — “No nervous system has yet been discovered 
in any of these animals ” f. 
[Postscript I. — Since this paper was presented to the Royal Society, Professor 
Huxley has been kind enough to direct my attention to an important memoir on 
the Medusae, which I had not previously read. This memoir is by Prof. Haeckel 
and in it he assigns special importance to his careful researches into the histology of 
the nervous tissues. The following is an epitome of his results, so far as they bear upon 
the subject of the present paper. 
After stating the conflicting views held by Agassiz, M‘Crady, Fritz Muller, Leuckart, 
Kefersteix, Ehlers, Claus, and others concerning the existence of a nervous system 
in Medusae, Prof. Haeckel proceeds to state that his own observations with reference to 
this subject do not agree with those of any previous writers. These observations were 
chiefly made upon the Geryonidce — a group of naked-eyed Medusae which, according to 
this naturalist, present exceptionable facilities for demonstrating the presence of nervous 
elements by means of microscopical research. In their distribution these elements 
are described as forming a continuous circle all round the margin of the nectocalyx, 
following the course of the radial canals throughout their entire length, and proceeding 
also to the tentacles and to the marginal bodies. At the base of each tentacle there is 
* Prof. L. Agassiz “ On tlie Naked-eyed Medusse of the shores of Massachusetts in their perfect state of Deve- 
lopment : ” see Memoirs of the American Academy of Arts and Sciences, new series, vol. iv. part ii. pp. 232, 
233 (Cambridge and Boston : Metcalf and Co., 1850). 
t Huxley, ‘ Classification of Animals.’ 
$ Beitrage zur Naturgeschichte der Hydromedusen, von Dr. E. Haeckel (Leipzig, 1865). 
