XI. The Croonian lecture.--Preliminary observations on the locomotor system of medusæ

Abstract

1. Structure of the Medusæ . -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 the Medusæ, 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 Medusæ 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 carefully 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 intervening 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 elongated 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 have already traced in all its details, as here described, in the genera Hippocrene ( Bougainvillia ), Tiaropsis , and Staurophora ”.