VOL. XC.] PHILOSOPHICAL TRANSACTIONS. J\\ 



when in a recent state; for the gristly part of the bulbs is then most probably much 

 softer, and more elastic, than it appears to be in the dried specimens which are 

 found in collections*. This gristly substance which forms the bulbs, and the 

 coralline joints, are kept together, and are covered, by a thin skin or membrane, 

 which is continued over the whole, like a tube. The joints are not therefore de- 

 void of a coating, as seems to be implied by the definition of Linnaeus. 



hit Hippuris. — Part of a branch of the isis was immersed in very dilute nitric 

 acid, and a considerable effervescence immediately took place. When this effer- 

 vescence had ceased, there appeared little or no change in the original form of the 

 isis; but the coralline joints were now become a soft, compact, white, and opaque 

 membranaceous substance; while the dark brown intermediate parts retained also their 

 form, and in other characters resembled those of horn. The solution was colour- 

 less and transparent. When saturated with pure ammonia, it was not affected; 

 but carbonate of pot-ash produced a copious precipitate of carbonate of lime. 

 Another part of this isis was exposed to a low red heat, in a crucible. The dark 

 brown horny parts swelled, and puffed up, with much smoke, and a smell like 

 that of burnt horn. The coralline joints also emitted the same smoke and smell, 

 and became dark gray. When put into dilute nitric acid, a solution was made, 

 with effervescence, during which, there was a copious deposition of animal coal. 

 From this solution, nothing but carbonate of lime was obtained by the usual pre- 

 cipitants. A tube of membrane invests the curious structure of the isis ochracea; 

 but no such tube or outer coat exists in the isis hippuris ; for the coralline joints, 

 like those of the madrepores, millepores, &c. consists of a membranaceous substance, 

 hardened by carbonate of lime, and the only difference appears to be ; that in the 

 madrepores and millepores, the membranaceous part is less compact and abundant; 

 but even the striae of the coralline joints remain visible, and unchanged, in the 

 membrane of this isis. The brown horny part forms also a marked characteristic 

 in this isis, and seems to approach it to certain of the gorgoniae. This horny part 

 does not however pervade the whole of the branch ; for where the coralline joints 

 commence, this horny substance immediately terminates, internally as well as ex- 

 ternally, and is not to be discovered but between or in the separation of these 

 joints. 



Gorgonia nobilis. — I next proceeded to examine the gorgonia nobilis or red coral ; 

 and of this I separately subjected to experiment different pieces, some of which 

 were polished, and deprived of their external pale red mealy coat, while others 

 were in their original state. A piece of the unpolished red coral being put into 

 dilute nitric acid, an effervescence immediately took place; and after some hours 

 the whole of the calcareous substance was completely dissolved. The external coat 

 retained the original figure, and appeared like a pale yellow tubulated membrane, 



• It must here be observed, that the articulated structure above-mentioned, is not to be found in 

 those parts which form the main stem, with its larger branches; the joints in those parts being consoli- 

 dated, so as to constitute a strong and rigid trunk, on which the whole fabric is supported. — Orig. 



