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Show 1884.] PROF. F.J. BELL ON HOLOTHUBOIDS. 565 pointed out at the time in ' Nature,' * about as much had been expelled as would occupy the greater part of the cloacal cavity. The information forwarded to me by Mrs. Fisher, and reported in the same journal2, is further evidence that the Holothurian is capable of emitting threads which are disagreeable to the human skin at any rate. The histological character of these tubes has been so fully worked out by M . Jourdain and Dr. Hamann in the essays to which reference has already been made that it is unnecessary here to enter into a detailed account. I have to say, however, that what has most struck me in the tubes of II. nigra has been the great abundance of the connective tissue. When a tube has been drawn out to its utmost tenuity, so fine indeed as to be almost invisible to the naked eye, it is seen under a magnifying-power of 500 diameters to consist of several fine fibres ; a somewhat thicker portion differs only in having the fine fibres more closely packed together. It seems, then, to be pretty clear that the elongation of the threads is due to the uncoiling of the connective-tissue fibres. When thus uncoiled they appear to have no outer epithelial coating, and it is therefore difficult to understand how they can be sticky if the glands figured by Hamann have the function that he ascribes to them. This is a point, however, that can only be worked out with living specimens, the threads in situ, extended, and elongated being severally aud comparatively examined. In all the specimens whose intestinal tracts were examined these organs were found to have contents formed of a slaty-grey pultaceous mass, clearly made up of decomposing material ; I got no such evidence of the character of the food as was presented to Mr. Peach. With regard to the name that should be applied to the Cotton- Spinner, the Rev. Dr. Norman informs me that he is of opinion that II. nigra is a synonym of H. poli of Delle Chiaje, or H. tubulosa of Sars. I cannot, however, in fresh, any more than in specimens long since preserved in spirit, detect the large spicules in the suckers by which the Mediterranean species is, as is well known, to be detected. I am greatly indebted to the reverend naturalist for reminding me that Holothuria intestinalis was dredged in the Minch by Forbes and Goodsir in 1850 3, and by himself in the same locality in 1866 4; so that "H. nigra " has a fellow in the British Seas. 1 Aug. 7, 1884, p. 335. 2 June 26. p. 193. 3 Trans. Roy. Soc. Edinb. xx. p. 309, pi. ix. fig. 1. 4 Rep. Brit. Assoc. 1866, p. 195. |