The finest sponges in the Mediterranean, those of the Levant and off the Syrian and Tripoli coasts, are found between the average aerial temperatures of 17° and 21° (63°-70° F.), and the isochrymals of 10°-14° (50°-57° F.), aud probably at no time of the year are these, which occur in the deeper water at a distance from the coast, exposed to a lower temperature than 15i° (60° F.). Io America, the whole region favourable to the production of the commercial qualities lies between St. Marks, on the coast of Florida, with an isotherm for January of 171° (63i° F.), and the equatorial isotherm for January of 27° (80° F.); south of this equatorial isotherm, however, the limits have not been ascertained, the data, both as regards the sponges and the temperatures, being deficient. The finer sorts are only found along the W. coast of Florida, among the Keys, and in the insular waters of the Baharna and Caribbean Islands. Their absence from a large part of the shore of the Gulf of Mexico may be attributed to the sandy or soft character of the coast, the silt of the Mississippi, and the absence of outlying islands ; the opeo and sandy or clayey character of the Atlantic coast northward to New York explains their non-occurrence there.
The sponges of the Red Sea are inferior to and rarer than those of the Mediterranean ; they most resemble the zimocca kind, the skeleton being blittle, entirely red, and very dark at the base ; and the two sorts are sold mixed. It therefore seerns that the high temperature of the Red Sea, in presence of perfectly clear water, is not so detrimental as where the waters are more loaded with sediment, as in the shallows of the Florida coast, or the specimens could not be sold com mercially in the company of even the ioferior Mediterranean qualities. The few true Australian Spongice are coarse, and have an excessively dark rough skeleton. The Sydney sponges, found under the marine isoehryrnal of 62° F., on an open and unfavourable coast, are presumably beach specimens, drifted from the coast of Queensland, which, inside the great boundary reef, is probably exceedingly favourable to the growth of the true Spongice. From all the ascertained facts, Hyatt deduces five rules as governing the quality of commercial sponges :—(1) The inferiority of the skeleton, which is common at Key West, with the same isochrynial as the Red Sea, is not found in the same degree in the sponges growing in the clearer waters of the latter; (2) the coarsest qualities of all the Mediterranean sponges, the " Gerbis " and others, grow in localities along the coast, where they are most subject to the action of suspended matter ia the water ; (3) but all of these are, on account of the clearness and medium temperature of the Mediterranean waters, as compared with those of other seas, of much finer quality ; (4) tbe coarser kinds of the same quality or variety grow nearest the shore, and the finer kinds in deeper water, and, according to Nassau (Bahamas) spongers, are more apt to occur upon marly ground, where the sediment is fiaer than upon other kinds of bottom; (5) the inverse ratio betweea the quantity, and even the prevalence, of different kinds of sediment, such as sand grains or spicules, and the resiliency and flexibility of tbe fibres of the sponge, may be demonstrated with tbe microscope in any series of specimens.
The openness or apertion which nsually accompanies and appears to correlate with the coarse ness of fibre cannot be accounted for in this complicated way, but must be considered as au element of inferioi ity always accompanying a skeleton having loose microscopical texture or mesh, and harsh, inelastic, enstly torn fibres ; hut it is also, though rarely, found in specimens of very fine quality, especially at an early ago. It is a common characteristic of all inferior qualities of Mediterranean, and of all Caribbean commercial spongea without exception ; the latter, whether with very fine or very coareo and inelastic fibres, are always permeated in the interior, and have the surface also cut up, by larger and more numerous canals than the corresponding Mediterranean species. The Australian Spongia spp., though coarser in fibre than the Caribbean, arc equally open, and usually much harder when dry. The evidence afforded by unmarketable varieties found in very hot climates, aud itll of which have very open, coarse, and brittle akeletons, confirms the opinion that this charac teristic of apertion may with good reaeon be attributed perhaps exclusively to the influence of unfavourable temperature, which may be either a degree of cold iudieated by an isotherm of about 50° F. for the coldeet montha, or the equally injurious heat shown by an average for the same mouths of t;5°--80° F.
With regard to colour, a darkening of the fibres about the base, and frequently of the whole sponge, may occur with any of the inferior qualities in any cold climate or unfavourable situation, as at Ietria, and varies with the age and size of the specin3en. These influences, however, never produce so marked an effect aa in a hotter climate, nor doea the deterioration of the fibre and of the density of the skeleton go so far; neverthelees, the Nassau eponges, which are lighter coloured than the Gerbis, and the foregoing remarke upon the influence of euepended matter near the shore, point to the fact that heat does not entirely control the colour, though it may largely influence it. Another point in this connection ia tbat the deepest colour ie always in the interior, and the lightest coloured parts are external, in the position most exposed to the action of light ; and this, though not necessarily, is probably the hottest part of the organism during the heated term of the year in the shallower waters, vvhere the darkest-coloured forms are mostly found. It haa been auggeeted that this coloration wae due to irou in the sediment or eca-bottem ; but this could hardly be the case in the vicinity of coral reefs, and the dark internal coloration appears to result from or corre late with the deterioration of the skeleton aa an internal change in structure, val.) ing with the species, the age, and the health of the specimen, and probably with the chemical composition of the fibres themaelves.