56 ZOOPHYTES. 



Porpita and Velella, though different in its cellular texture. Ex- 

 cluding these doubtful instances, foot-secretions are confined to the 

 group Alcyonaria, and the single genus Antipathes among tlie 

 Actinaria. 



50. Che7nical Constitution of Coral Secretions. We find as early 

 as in Marsigli, the results of some experiment! ngs on corals, in tlie 

 rude chemical methods of the day ; but the first examinations of any 

 value, are those by Charles Hatchett, in the Philosophical Trans- 

 actions, for 1800 ;* and these give us at the present time the 

 most definite information hitherto published with regard to these 

 secretions. 



Mr. Hatchett found the stony corals, as far as he examined them, 

 to consist of carbonate of lime, with some fibrous membranes or "loose 

 gelatinous substance," which, in certain species (Dendrophyllia ramea, 

 Myriozoon truncatum), retained, in some degree, the form of the 

 coral after its digestion in nitric acid. In a Nullipora, (now classed 

 with the vegetable kingdom,) he found, besides carbonic acid, a small 

 proportion of phosphoric acid, together with a substance retaining 

 the form of the nuUipore, " of which a strong white opaque mem- 

 brane formed the external part, and a transparent gelatinous sub- 

 stance the interior." 



His observations were most extensive with the Alcyonia tribe. 

 The horny axis of the GorgonidiE afforded him generally a large pro- 

 portion of cartilage, with some phosphate and carbonate of lime. In 

 the Gorgonia ceratophyta, and flabellum, the proportion of phosphate 

 was large, and, in one species, the composition was very near that of 

 stag-horn. While in others, the G. umbraculum, verrucosa, &c., he 

 found no phosphate. The cortex in these zoophytes consists largely 

 of animal membrane, with much carbonate of lime, and, in some 

 instances, a trace of phosphate. The tubes of a Tubipora afforded a 

 like constitution without phosphoric acid, and the Corallium, the same, 

 with a small portion of phosphate. The red colour of these species 

 was destroyed by the acid, but that of a Melitasa was precipitated in 

 nitric acid as a fine red powder. 



Mr. Hatchett concludes, from his investigations, that corals, bone, 

 and horn, have an analogous constitution differing only in the propor- 

 tion of the ossifying ingredients. 



Mr. J. E. Gray has shown that the interior of some Gorgonidee 



* Philosophical Transactions abridged, vol. xviii., pp. 706, 725. 



