12'L PHILOSOPHICAL TRANSACTIONS. [ANNO 1800. 



however, a completely formed membrane or cartilage was left, retaining the figure 

 of the original bone. 



When therefore the component parts of shell and bone are considered, it ap- 

 pears that the essential characteristics are, carbonate of lime for the one, and 

 phosphate of lime for the other ; and that their bases consist of the modifications 

 of a glutinous, gelatinous, or membranaceous substance. I experienced much 

 gratification in tracing the progressive and connected changes in the composition of 

 the various shells and bones; and a considerable increase of pleasure arose, in 

 proportion as the observations made on those bodies were corroborated, and the 

 chain of connection extended, by the developement of the facts resulting from the 

 experiments on zoophytes, which form the principal subject of this paper. 



It will now be proper to review these experiments, and to examine how far they 

 agree with those made on shell and bone, and how far they tend to prove, that 

 these substances are all of a nature closely connected. The experiments on the 

 madrepores afforded the following results. Madrepora virginea, when examined 

 by acids, left but very little of any gelatinous substance or membrane. M. muri- 

 cata, and M. labyrinthica, afforded loose portions of a transparent gelatinous sub- 

 stance. M. ramea, and M. fascicularis, when deprived of the carbonate of lime 

 by acids, remained in the state of completely organized membranaceous bodies, 

 which exhibited the original figure of the respective madrepores ; and the propor- 

 tion of coal afforded by these last, was more abundant than what was obtained 

 from those which were first mentioned. 



To these succeeded the experiments on the miliepores ; from which it appeared, 

 that millepora caerulea afforded loose detached portions of a gelatinous substance. 

 M. alcicornis yielded the same, but in a more coherent state. M. polymorpha 

 remained unchanged in shape, and consisted of a strong white opaque membrane, 

 filled with a transparent jelly. Lastly, M. cellulosa, M. fascialis, and M. truncata 

 afforded membranaceous bodies, in a complete state of organization ; and all these 

 miliepores, when exposed to a low red heat, yielded various quantities of coal, 

 according to the greater or less abundance of the gelatinous or membranaceous 

 substance. 



The universal, and only hardening principle of these madrepores and miliepores, 

 was proved to be carbonate of lime, with the single exception of millepora poly- 

 morpha, which also appears to be differently constructed from the other millepora?. 

 With this single exception, carbonate of lime seems to be the only hardening sub- 

 stance in these bodies ; and when every circumstance is considered, an exact simi- 

 larity is to be found between the substance forming the various shells, and that 

 which forms the madrepora? and milleporae ; and the nature of these bodies is so 

 completely the same, that the changes or gradations of the one are to be found in 

 the other. For the chemical characters which distinguish the porcellaneous shells, 

 are in a great measure approached by those of madrepora virginea ; and those 

 which were noticed in the patellae, correspond precisely with the madrepores and 



