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 the 
Actinaria. 
50. Chemical Constitution of Coral Secretions. We find as early 
as in Marsigli, the results of some experimentings on corals, in the 
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. Ina 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 nullipore, “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 Gorgonide 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 Melitaa 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 Gorgonide 
@ 
* Philosophical Transactions abridged, vol. xviii., pp. 706, 725. 
