logical work. But, as the physiology of the subject continued to open up in the wonderful way in which it did, I felt it was undesirable either, on the one hand, to suspend this part of the inquiry, or, on the other hand, any longer to defer a thorough investigation of the histological part. I therefore represented the case to my friend Mr. Schäfer, who very kindly consented to join me in Scotland with the view of coöperating with me in the research. The histological results which he has obtained from a most skillful and painstaking investigation are in the highest degree interesting. He worked chiefly with Aurelia aurita and found that the tissue which performs the ganglionic function in the marginal bodies is of the nature of modified epithelium-cells, the ganglionic function of which could scarcely have been suspected but for the paralyzing effects which are produced by their excision. From these marginal ganglia there radiate what he regards as delicate pale nerve-fibres, which sometimes present the appearance of fibrillation.
These fibres spread over the entire expanse of the muscular sheet in 
Fig. 2. great numbers. It will thus be seen that these microscopical researches of Mr. Schäfer fully bear out my inference from the result of physiological experiments, which was previously published at the Royal Society—the inference, namely, that the entire muscular sheet of the Medusæ is overspread by a dense plexus of nervous channels. But these researches of Mr. Schäfer tend to negative another inference which was published at the Royal Institution—the inference, namely, as to the degree in which these channels are differentiated.[1] As the facts on which this inference was based have not been previously published in the Fortnightly Review, and as, apart from the dubious inference, they are facts of the first importance, it is necessary that I should here very briefly restate them. The annexed woodcut (Fig. 3) represents a specimen of Aurelia aurita with its polypite cut off at the base, and the under or concave surface of the bell exposed to view. The bell, when fully expanded, as here represented, is about the size of a soup-plate, and in it all
- ↑ I may here state that, previous to Mr. Schäfer's researches, I had observed both the tissue-elements which he describes; but I hesitated to pronounce upon their nervous character. It will thus be understood that even now, without wishing to dispute the accuracy of his judgment in this matter, I do wish it to be known that the responsibility of this judgment rests entirely with my friend.
