OCR Text |
Show 1868.] DR. J. E. GRAY ON THE CERATELLADJE. 577 slightest indication of such a covering to be observed in any of the specimens I have examined; but that is also the case in the Porites and sponges that are generally found in collections. The younger parts of these plant-like animals are formed of agglutinated, free, horny, projecting fibres, and the older parts of keratose network; so that it is probable that, as part of the animal becomes old, or only required for the support of the young or more lately developed portion, the projecting portions become gradually transformed into a horny network. I have not been able to discover, in the very cursory microscopic examination of these specimens which the state of m y eyes will allow me to make, any appearance of aquiferous canals in the stem or branches, such as one might expect to exist if they are sponges, or if the prominences on the branches are oscules ; nor have I been able to observe any indications of any lamellar star-like cavities either in the prominences or cells on the branches, or in the substance of the stems or branches, which ought to be there if they are madrepore corals allied to Porites, even supposing that a horny coral does exist; and a horny madrepore coral would be a very aberrant form. A sponge has been described under the name of Darwinella which is said to be made up of horny spicules; but I have not seen this sponge, aud do not know the remainder of its structure. I have requested Mr. M . E. Cooke to undertake to examine the microscopic structure of these specimens, which the state of m y eyes will not allow m e to attempt. He states that he has not been able to discover any siliceous spicules. The absence of any lacunae in the structure of the stem or branches, or communication with the cell for the circulation of the water, which ought, according to the idea of its being a sponge, to be emitted by the cell-like oscules (and the regular development of the cell is much more like the budding of a fully developed polype than the growth of a Protozoon or sponge), leads one to doubt its proper arrangement with them. At the same time, the want of the cylindrical cells for the bodies of the actinoid polypes is equally repugnant to the idea of its being a horny madreporoid coral. There can be no doubt that though the two specimens of these animals which I have examined are sufficiently different from each other in structure and growth to be regarded as belonging to two genera, yet they are so allied as to form a single family, which 1 propose to call C E R A T E L L A D ^ E . The family may be characterized by the details which I have already given of their structure. CERATELLA. Sponge or coral irregularly dichotomously branched, more or less expanded on a plane from a single base; of a dark brown colour, of a uniform, hard, horny substance; stem hard, dark brown, solid ; base dilated, rather compressed, of a uniform rigid somewhat spongy texture, with a velvety surface, which is formed of an abundance of very minute, cylindrical, tortuous grooves. The branches and branchlets tapering, formed of a very large quantity of nearly parallel, |