VOL. XC.] PHILOSOPHICAL TRANSACTIONS. 723 



millepores which afford a gelatinous substance ; and lastly, the characters of the 

 membranaceous part, exhibited by the shells formed of nacre or mother of pearl, 

 are in like manner to be found among some of the madrepores and millepores, 

 such as madrepora ramea, millepora fascialis, millepora truncata ; for these, like 

 the turbo olearius and haliotis iris, are composed of a fibrous membrane, hardened 

 by carbonate of lime. It appears therefore, that the madrepores and millepores, 

 like the various shells, are formed of a gelatinous or membranaceous substance, 

 hardened by carbonate of lime ; and the only difference is in the mode according 

 to which thest. materials have been employed. 



The experiments on tubipora musica proved, that in composition it resembled 

 the foregoing substances. But a slight difference was observed, in respect to the 

 hardening substance of flustra foliacea and corallina opuntia ; for a small portion 

 of phosphate was found mixed with the carbonate of lime ; but the membrana- 

 ceous part of these bodies resembled that of certain madrepores and millepores, 

 particularly millepora fascialis. Two species of isis were next examined, namely, 

 isis ochracea and isis hippuris : both of these were proved to be formed of regularly 

 organised membranaceous, cartilaginous, and horny substances, hardened, in the 

 last mentioned species, merely by carbonate of lime ; but, in the isis ochracea, 

 with the addition of a very small portion of phosphate of lime. 



The subsequent experiments were made on various species of gorgonia, and first 

 on gorgonia nobilis, which was formerly regarded as an isis. The hardening sub- 

 stance of this was found to be carbonate of lime, with a small portion of* phosphate ; 

 but the matter forming the membranaceous part was, like that of millepora poly- 

 morpha, in 2 states ; that of the interior being gelatinous ; and that of the exter- 

 nal part being a membrane completely formed, so as to cover the stem, in the 

 manner of a tube. The results of the experiments on certain gorgoniae, such as 

 ceratophyta, flabellum, suberosa, pectinata, and setosa, were not a little remark- 

 able ; for, " when the 2 parts which compose these gorgoniae, namely, the horny 

 stem, and the cortical substance by which it is coated, were separately examined, it 

 was proved, 1st. That the stems of these gorgoniae consist of a substance analo- 

 gous to horn ; and that, by long maceration in diluted nitric acid, this horny sub- 

 stance becomes soft and transparent, so as to resemble a cartilaginous or tendinous 

 body ; also the stems of these gorgoniae afford a quantity of phosphate of lime, 

 but scarcely any trace of carbonate. 2dly. That the cortical part, on the contrary, 

 consists principally of carbonate of lime, with very little or none of the phosphate; 

 and the carbonate of lime is deposited in and upon a soft flexible membranaceous 

 substance, which seems much to approach the nature of cuticle. 



Some other gorgoniae, which were subsequently examined, and which much 

 resembled the former construction, did not yield any phosphate of lime ; but in 

 every other particular they proved to be similar. The gorgonia antipathes was 

 found to be entirely formed of a fibrous membrane; and the black shining polished 

 gorgonia afforded, by maceration, a most beautiful specimen of membranes con- 



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