120 DR. J, K. GRAY ON HYALONEMA LUSITANICUM. [Jail. 24, 



the polypes with which it is covered as a species of Pahjthoa ; and 

 Professor Max Schultze has sujjported this theory by a microscopic 

 exaniiiiation of the spicules of the sponge, of the axis, and the bark 

 or corivm*. 



Some of the arguments in favour of this view of the question may 

 be thus condensed : — 



I. Silica is not exclusive!]/ secreted by sponges, as the advocates of 

 the spo)iye-theory seem to believe, but is found mixed with corneous 

 matter {as it is mixed in Hyalonema and Euplectella) in Gorgonia 

 atid Antipathes, and with calcareous matter in Madrepores. 



Mr. (Children, in my paper "On the Chemical Structure of 

 Sponges" (see Annals of Philosophy, 1825, ix. p. 431), in which I 

 first showed that the spicules of some sponges are composed of silica, 

 states that he found sufficient silica in the carefully prepared ashes 

 of the axis of Goryonia flahellum to form a globule before the blow- 

 pipe. This proves that silica is found in the coral of the Alcyonaria 

 or polypes with pinnate tentacles. 



Professor U. SilHman, in the " Appendix to Dana, on the Struc- 

 ture and Classification of Zoophytes," states that in three genera of 

 Madrepores ( Madreporaj-ia) which he examined he found that one 

 contained nearly 9, another 12, and a third 23 per cent, of silica ; he 

 further states that " the silica exists in the coral in its soluble modi- 

 fication, and probably united to the lime." If nearly one-quarter of 

 the solid parts of a calcareous coral of a zoanthoid polype consists of 

 silica, there can be no reason that a zoanthoid polype might not pro- 

 duce a coral of pure silica without any calcareous material. 



M. Mihie-Edwards calls one genus of Antipathidse Hyalopathes, 

 because the axis is smooth and has a vitreous appearance ; i'urther, 

 he believes that the axis differs in chemical composition from that of 

 the other genera of Antipathidae (see-CoraUiaires, vol. i. p. 323). I 

 have not seen this genus ; but it is to be observed that he forms for 

 the Antipathes a group which he calls Zoanthaires sclercbasiques, 

 and it is to this group that the Hyaloneniidse must be referred ; 

 indeed, from the manner in which M. Milne-Edwards refers to the 

 genus, this is where he would have placed it if he had not been in- 

 formed by M. Valenciennes that he considered it a sponge with a 

 parai^itic Zoantkus. 



II. The structure of the siliceous spicules of sponges is very simi- 

 lar to, almost identical with, the sti'ucture of the axis of Gorgonia 



* Tlie truth of Dr. Bowerbank's assertion (also supported by Dr. Wiliiani Car- 

 peuter), that the zoanthoid polype of this coral, described by Brandt, Schultze, 

 Boca^e, and myself, is only the oscxile of the sponge, can be at once disproved 

 hy the examination of a si)ecimen, or the study of the works of the authors cited, 

 and can scarcely be considered an object of discussion. It is true Dr. Bowerbank 

 has written a long and diffuse paper to attempt to prove his position, when a 

 cut in the polype-cell could have settled the question. It is a pity he did not 

 recollect King Charles's question about the fish and the water. I have made 

 some observations on M. Valenciennes's and Dr. Bowerbank's theories in the 

 'Annals and Magazine of Natural History ' for 1866, vol. .wiii. 



