The severed margin continues its rhythmical contractions for two or three days. I am now trying the effect of different chemical stimuli, and if you can suggest any further line of experimentation, of course I shall be very pleased. Only, if you can think of anything which might be tried and which is not mentioned in this letter, please write soon, as the Sarsia will not last much longer, and they are the best adapted for my purposes. I remain, very sincerely yours, GEO. J. ROMANES. P.S.--I should have said that neither gold nor silver brings out any nervous tissue. Medusa muscle is not doubly refracting, but then none that I have here seen is striated, and unstriated muscle is not doubly refracting anywhere, is it? Dunskaith: June 24. Many thanks for your long and suggestive letter. The poisons also are most acceptable. I have waited before writing to try effect of the latter, but the weather has been so stormy that no jelly-fish could be got. The most interesting observations I have made since writing before are the following. Unmutilated Sarsia in a dark room seek a beam of light thrown into the bell-jar containing them, and this as keenly as do moths. But when the so-called eye-specks are cut out, the animal no longer cares for light. I have only come across two species of luminous Medusæ--both, I believe, as yet undescribed--and in these the light is emitted from the margin alone, and, with electrical stimulus, is strictly confined to the intra-polar regions, being strongest at the two poles. There is no doubt at all about the muscular nature of the fibres we saw. In the larger kinds of Medusæ (the covered-eyed) these fibres are much coarser, and are clearly seen to be arranged in concentric bundles, having four or five fibres in each bundle. Alternating with these bundles, and about the same width as these, are strands of undifferentiated protoplasm. These strands are not spontaneously contractile, although their dimensions are altered by the contraction of the muscular branch on each of their sides. No part of the tissue is doubly refracting in the fresh state. Is there any way of treating it with a view of bringing out this property if latent, so to speak? The peculiarity is not due to the _transparency_ of the tissue, for I find that the muscular fibre of the transparent osseous fish _Leptocephalus_ is as doubly-refracting as could be wished. There are no signs of striæ, but Agassiz says that in some of the Mediterranean species striæ are well marked. But if both striated and unstriated fibres are elsewhere doubly-refracting, it does not, I suppose, much signify whether or not the muscles of Medusæ are striated--so far, I mean, as the peculiarity in question is concerned.