| OCR Text |
Show 1886.] POSITION AND CLASSIFICATION OF SPONGES. 573 we have Ceraospongiae before us. Transitional forms between the Cornacuspongiae with supporting spicules cemented by spongin, and Cornacuspongiae without spicules in their fibres (horny sponges), are not unfrequent. One whole subfamily, the Chalininae, comprising nearly 300 species, is composed of such transitional forms. Tbe supporting spicules met with in the Cornacuspongiae are invariably monaxon without a swelling at one end. Besides these more or less rod-shaped supporting spicules, we also find in some of the Sponges belonging to this group so-called flesh-spicules-small, irregular curved or complicated elements scattered throughout the Mesogloea. These occur associated with spicules in the fibrous supporting skeleton and also in those forms which have no spicules in their horny supporting skeleton. To this group also the genera Halisarca and Bayalus belong, which have no skeleton at all, and appear as askeletous forms of the Aplysillide type. The term Cornacuspongiae was established by Vosmaer (1550), and used by him in a very similar sense to that in which it is used here. The group Chondrospongiae, on the other hand, is in the sense given above a new one ; it nearly coincides with Vosmaer's group Spiculispongiae (1550). In a former paper (889) I had retained the group Myxospongiae, for the sake of convenience, preliminarily only, and agreeing at tbe time with Sollas (1440) that it was unnatural. The manner in which I have distributed the members of the Myxospongiae among other groups is in accordance with the view expressed by F. E. Schulze in a letter. W e have accordingly to divide the subclass Silicea into three groups in the following manner :- Subclassis SILICEA, Lendenfeld. Mesoglcea soft; supporting skeleton often strengthened with siliceous cement. Spicules triaxon. Ordo HEXACTINELLIDA, O. Schmidt. Mesoglcea bard; toughness achieved by the hardening of tbe ground-substance. Spicules tetraxon, monaxon, anaxon, or absent ; generally corticate. 3. Ordo CHONDEO-SPONGLE, Lendenfeld. Mesoglcea soft; supporting skeleton strengthened by spongin cement; or exclusively formed of spongin, with or without foreign bodies. Spicules monaxon, or absent. 4. Ordo CORNACU-SPONGT. E, Vosmaer. Expressed in the usual manner, the class Spongiae would be accordingly divided mto four Orders in the following manner:- Classis SPONGIiE, auctorum. Coelentera with branching canal-system, without movable appendages ; the organs of which are developed from cells of the mesogloea. With simple epithelia. I. Subclassis CALCAREA, Grant. Spongiae with a skeleton composed of spicules which consist chiefly of carbonate of lime. |
