VOL. XC.] PHILOSOPHICAL TRANSACTIONS. 707 



substances. On the view therefore of these facts it is evident, that there is a great 

 similarity in the construction of shell and bone; and that there is even an ap- 

 proximation in the nature of their composition, by the intermediate crustaceous 

 substances. 



These remarks, with the experiments by which they are supported, form the 

 principal features of that paper, which was honoured with a place in the last vol. 

 of the Phil. Trans. At that time, it was not my intention immediately to pursue 

 the subject; but I changed this resolution, after a conversation with Dr. Gray, 

 Sec. e. s., who suggested, that many marine substances still remained to be ex- 

 amined in a similar manner; and that a series of experiments on zoophytes, 

 hitherto but little known in respect to their component parts, would be very in- 

 teresting, and might probably lead to some improvement in their classification. I 

 was therefore induced to make the experiments contained in the following pages; 

 and as the mode adopted was very similar to that which was formerly pursued, it 

 appears superfluous here to repeat the description. It will be proper however to 

 observe, that argill is not unfrequently lodged, as an extraneous substance, in the 

 interstices of many of the madrepores, and such like bodies; and, as argill is pre- 

 cipitated by pure ammonia, it became necessary not to rely merely on the ammo- 

 nia, as a test of phosphate of lime. Whenever therefore any precipitate was pro- 

 duced by ammonia, it was dissolved again in acetous acid, and this solution was 

 examined by the addition of acetite of lead. 



§ 1. EXPERIMENTS ON ZOOPHYTES. 



Madrepora virginea*. — This madrepore, when immersed in very dilute nitric 

 acid, effervesced much, and was soon dissolved. The solution was perfectly trans- 

 parent and colourless, with but a small appearance of gelatinous or membranaceous 

 particles. Pure ammonia was then added, but did not cause any alteration; and 

 the whole of what had been dissolved, was afterwards completely precipitated by 

 carbonate of ammonia, and proved to be carbonate of lime. 



Madrepora muricata. — When treated like the former, this afforded some loose 

 particles of a gelatinous substance: these were separated by a filter, and the 

 solution was supersaturated with pure ammonia, without effect; but on adding car- 

 bonate of ammonia, the dissolved part was precipitated, in the state of carbonate 

 of lime. 



Madrepora labyrinthica. — This, being examined in the manner above-mentioned, 

 proved to be composed of carbonate of lime, and of a loose gelatinous substance, 

 similar to that afforded by madrepora muricata. 



Madrepora ramea. — When this madrepore was first immersed in very dilute 

 nitric acid, a considerable effervescence was produced ; and after a few hours a pale 

 brown fibrous membrane remained, which in some measure exhibited the original 



* The different species are named according to Gmelin's edition of Linnaeus's Systema 

 Naturae.— Orig. 



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