Text-book of comparative anatomy . iibcr Orthoncctiden. Zeitschr. f. wiss. Zoologie. Bd. 35. 1881. Julin. Contribution it Vhistoire dcs Mesozoaires. Archives de Biologic. T. F. E. Schulze. Ucbcr Trichoplax, adhaerens. Zoolog. Anzcigcr. Bd. VI. 1883. S. 92-97. CLASS II. Porifera or Review. Sub-Class I. Calcaria.—Skeleton composed of spicules of carbonate of lime,always present. According to the structure of the soft body, Ascones, Sycones, andLeucones. Olynthus, Ascandra, Sycandra, Lcucandra. Order 1. Calcispongise. Sub-Class II. Non-Calcarea.—Skeleton seldom wantin
Text-book of comparative anatomy . iibcr Orthoncctiden. Zeitschr. f. wiss. Zoologie. Bd. 35. 1881. Julin. Contribution it Vhistoire dcs Mesozoaires. Archives de Biologic. T. F. E. Schulze. Ucbcr Trichoplax, adhaerens. Zoolog. Anzcigcr. Bd. VI. 1883. S. 92-97. CLASS II. Porifera or Review. Sub-Class I. Calcaria.—Skeleton composed of spicules of carbonate of lime,always present. According to the structure of the soft body, Ascones, Sycones, andLeucones. Olynthus, Ascandra, Sycandra, Lcucandra. Order 1. Calcispongise. Sub-Class II. Non-Calcarea.—Skeleton seldom wanting, but never of calcareousspicules, rather of siliceous spicules or spongin fibres. According to the structure ofthe soft body, Leucones. II POEIFERA Order 2. Hexactinellidse. 61 Siliceous needles, isolated or bound together by masses of silica into a continuousfirm framework, til-axial. Flagellate chambers cylindrical, placed radially, similarto the radial tubes of Sycandra. Most forms fossil. Living: Euplcctclla, FIG. 50.—Skeleton of a horn sponge attached to a stone, o, Oscula. Order 3. Spiculispongise. Skeleton consisting of independent siliceous spicules of various kinds, rarelywanting. The spicules are often bound together into bundles by an organic sub-stance, or form firmly connected skeletons interlocking by means of knotty out-growths ; they are, however, never cemented together by siliceous masses. Geodia,Plakina, Chondrosia, Oscarella, and Halisarca (without skeleton), Tethya, Tuberella,Subcrites. Order 4. Halichondrina. Skeleton composed of siliceous spicules, chiefly uniaxial, cemented together by amore or less horny substance (spongin). Halichondria, Reniera, Spongilla (in freshwater) Myxilla, Clathria. 62 COMPARATIVE ANATOMY CHAP. Order 5. Ceraspongiae (Fig. 56). Skeleton consists of horn fibres (spongin). Proper spicules wanting. Fragmentsof foreign spicules, sand, etc., are often used for strengthening. S^iongdia,Euspongm officinalis (bath sp
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