Elementary text-book of zoology, tr Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote elementarytextbo01clau Year: 1892-1893 FIG. 160.—Silex bodies from different silicious Sponges, a, Silex needle from SpowgiUa, inside the cell. J, Amphidisc of a gemmule of SpongiUa. c, Anchor from Ancorina. d, Hook from Egperia. c, Star from Chondrilla. f, \nckorfromEuplectella aspcrgiUum. g, h, needle rays from the same, i, Six-rayed needle from the same, with central canal. structure is commonly known as the collar, and the cells as the collared cells.]
Elementary text-book of zoology, tr Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote elementarytextbo01clau Year: 1892-1893 FIG. 160.—Silex bodies from different silicious Sponges, a, Silex needle from SpowgiUa, inside the cell. J, Amphidisc of a gemmule of SpongiUa. c, Anchor from Ancorina. d, Hook from Egperia. c, Star from Chondrilla. f, \nckorfromEuplectella aspcrgiUum. g, h, needle rays from the same, i, Six-rayed needle from the same, with central canal. structure is commonly known as the collar, and the cells as the collared cells.] The thick layer in which the skeletal spicules are produced consists of a hyaline matrix, in which irregularly branched or |Q spindle-shaped amoeboid cells are embedded, and may be regarded, like the gelatinous substance of the Acahpha, as mesoderm, while the external,.clearly defined, flat epi- thelium (also in the Asconia, Leucosolenia] is to be considered as ectoderm. The pores or inhalent openings so cha- racteristic of the Sponge bod}' are in reality only intercellular spaces, and are able to close themselves, vanish and be replaced by new pores, which arise by the separation of one cell from another (tig. 1G1). * Upon this ground Clark declared the Sponges to be nearly allied to tho Flaqdlata, arid regarded them as great colonies of the latter. FIG. 161.—Portion of the exter- nal ' ,S),,,wV>Y/,i \vith the pores, P (after Luburkiihn).
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