. An introduction to zoology, with directions for practical work (invertebrates). Fig. 28. âVarious forms of Sponge Spicules (from Parlcer and Haswell). spicules which are so very characteristic of sponges and give them their tough texture. These spicules are of very varied shapes in different sponges (Fig. 28); in those of the Ascon type they are usually three-rayed and calcareous. This very simple Ascon type of structure is found in no adult British sponge, but is a stage passed through by some of them, Clathrina blanca, the White Lattice Sponge, which has at this stage a minute vase-li
. An introduction to zoology, with directions for practical work (invertebrates). Fig. 28. âVarious forms of Sponge Spicules (from Parlcer and Haswell). spicules which are so very characteristic of sponges and give them their tough texture. These spicules are of very varied shapes in different sponges (Fig. 28); in those of the Ascon type they are usually three-rayed and calcareous. This very simple Ascon type of structure is found in no adult British sponge, but is a stage passed through by some of them, Clathrina blanca, the White Lattice Sponge, which has at this stage a minute vase-like body about x^-th of an inch high, similar in structure to that shown in Fig. 27. Later the sponge branches in a complicated way, forming a reticulate sponge body with several oscula. In Syeon, a British sponge to be found on the ^° â south coast, there is still only one single central chamber, but the wall is much thicker, and from the central cavity lateral branches extend regularly and radially into the wall; the flagellate collar cells are now restricted to these radial extensions of the central cavity which is itself lined merely by flattened endo- dermal cells (Fig. 29). A further complication is introduced by the outer skin cells being pushed in between two adjacent flagellate cham- bers, so that the external lateral pores open into a long narrow cavity which runs inwards between the flagellate chambers, and communicates with them laterally (Fig. 29, a). The water sucked in by the inhalent pores then passes down an incurrent canal, then on into a flagellate chamber, and finally into the central cavity and out of the osculum. In Sycons, as in Ascons, many spicules are present which. Fig. 29.âCross section through part of the wall of a Sycon. a, iDCurrent canal; the collar cells of the radial chambers are shown by short parallel lines (after Korschelt and Heider).. Please note that these images are extracted from scanned page images that may have been digitally enh
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Keywords: ., bookcentury1900, bookdecade1910, bookpublisherlondo, bookyear1913
