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XL The Croonian Lecture. — Preliminary Observations on the Locomotor System of 
Medusae. By George J. Romanes, M.A., F.L.S., &c. Communicated by Professor 
Huxley, LL.L., Sec. P.S., &c. 
Received November 1, — Read December 16, 1875. 
I. Structure and Movements of the Medusae. 
§ 1. Structure of the Medusae. — Although it is not my intention in this preliminary 
notice to enter into the literature of my subject, it is nevertheless desirable to quote the 
well-known statements of Prof. L. Agassiz regarding the nature and distribution of 
the nervous system which he describes as occurring in the Medusae. He says: — “There 
is unquestionably a nervous system in Medusae, but this nervous system does not form 
large central masses to which all the activity of the body is referred, or from which 
it emanates In Medusae the nervous system consists of a simple cord, of a 
string of ovate cells, forming a ring round the lower margin of the animal, extending 
from one eye-speck to the other, following the circular chymiferous tube, and also its 
vertical branches, round the upper portion of which they form another circle. The 
substance of this nervous system, however, is throughout cellular, and strictly so, and 
the cells are ovate. There is no appearance in any of its parts of true fibres. 
“I do not wonder, therefore, that the very existence of a nervous system in the 
Medusae should have been denied, and should not be at all surprised if it were even now 
further questioned. I would only urge those interested in this question to look care- 
fully along the inner margin of the chymiferous tubes, and to search there for a cord 
of cells of a peculiar ovate form, arranged in six or seven rows, forming a sort of string, 
or rather similar to a chain of ovate beads placed side by side and point to point, but in 
such a manner that the individual cells would overlap each other for one half, one 
third, or a quarter of their length, being from five to seven side by side at any given 
point upon a transverse section of the row ; and would ask those who do not recognize 
at once such a string as the nervous system to trace it for its whole extent, especially 
to the base of the eye-speck, where these cells accumulate in a larger heap, with inter- 
vening coloured pigment forming a sort of ganglion ; then, further, to follow it up 
along the inner side of the radiating chymiferous tubes which extend from the summit of 
the vault of the body, and to ascertain that here, again, it forms another circle round 
the central digestive cavity, from which other threads, or rather isolated series of elon- 
gated cells, run to the proboscis ; they will then be satisfied that this apparatus, in all 
its complication, is really a nervous system of a peculiar structure and adaptation, with 
peculiar relations to the other systems of organs and such a nervous system I 
MDCCCLXXVI. 2 Q 
