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Show 500 DR. J. E. GRAY ON SPONGES. [M^J 9, species in these genera have the spicules of that form, or with the forms so combined together. The modification of the forms and the comparative sizes of the different forms as combined together afford good characters for the distinction of the species of the genera or subgenera. There are more genera than I would willingly have made without more materials; but I could not exhibit the system which I wished to propose without forming some genera on very imperfect materials, as on a bihamate spicule figured in Bowerbank's ' British Sponges.' I have no doubt that some, indeed many, zoologists will complain of the numerous genera into which the sponges are here divided; but I believe that sponges will never be properly distinguished into species until they are even more closely divided into genera or subgenera than is here proposed. At least this has been shown to be the case with Diatomaceee, Algce, and the animals which require the microscope to distribute them into groups or species. N o part of the sponge seems so well adapted for the purpose of so dividing them as the spicules that form their skeleton, which afford, both in their form and in the combination of one or more forms of the same kind, the best characters for the separation of the sponges into genera and the distinction of the species. I may state that many of the names used for the genera have no derivations, but are mere fortuitous combinations of letters, so that compilers of indices of genera need not attempt to find derivations for them, or to correct the formation of some of them, as being more consistent with the derivations they may gratuitously assign to them, as has been done with some generic names of the same kind by Agassiz and others. It is only necessary to look at Dr. Bowerbank's work on 'British Sponges/ to show that some other system than that which he has adopted is necessary; for out of 193 species of British sponges no less than 43 are referred to the genus Isodictya, 42 to Hymeniaci-don, 28 to Halichondria, and 11 to Dictyocylindrus; so that 124 are referred to four genera, and the remaining 69 species are divided into 26 genera. Class PORIPHORA. Spongia, Linn. Amorphozoa, Blainville, Manuel Act. 1821. Poriphera, Grant, Outlines of Anat. 1841. Porifera, Bowerbank, Phil. Trans. 1850, p. 186; Brit. Sponges, 1862 ; Carpenter, Microscope, p. 536 (not Hogg, Ann. & Mao-. N. H. 1840, iv.). •• Porophora, Hogg, Ann. & Mag. N. H. 1840, iv. Gelatinifera, Hogg, Ann. & Mag. N. II. 1840, iv. Sqyongioitista, Hogg, Athenceum, 1867, p. 160. Spongiadce, Bowerbank, Brit. Sponges, 1864. The sponges consist of a flesh or sarcode formed of a°*o-reo-ations of amceba-like bodies, some of which are furnished with one or more |