. Elements of comparative anatomy. Anatomy, Comparative. SKELETON OF C<ELENTERATA. 105 Skeleton. § 81. In addition to the organs of support, which are formed by the above-mentioned tests, the Ccelenterata have various other forms of skeletons, which are differentiations of the mesoderm. There are none in the Physemariaa, which make up for the absence by taking up foreign bodies into their ectoderm j in the Porifera, some of which have no firm structures (Halisarcina), organs. Fig. 36. A portion of the surface of the body of a Calcareous Sponge (Sycaltis perforata) to show the triradiate spi
. Elements of comparative anatomy. Anatomy, Comparative. SKELETON OF C<ELENTERATA. 105 Skeleton. § 81. In addition to the organs of support, which are formed by the above-mentioned tests, the Ccelenterata have various other forms of skeletons, which are differentiations of the mesoderm. There are none in the Physemariaa, which make up for the absence by taking up foreign bodies into their ectoderm j in the Porifera, some of which have no firm structures (Halisarcina), organs. Fig. 36. A portion of the surface of the body of a Calcareous Sponge (Sycaltis perforata) to show the triradiate spicules, o Dermal ostia, each of them surrounded by a circlet of spicules (after Hackel). of support are formed by firm needles (spicula), or softer fibres, which are placed in the mesoderm. The former are formed of chalk, or of silica; the sponges are known accordingly as Calcareous or Siliceous sponges. The spicules of the Calcispongiee are simpler in character, for they are either acicular tri- or quadri-radiate; they present great regularity of distribution and arrangement, together with numerous modifications in individual characters. The above figure gives a representation of the spicula of a Calcareous Sponge. The hard structures, when formed of silica, are much more varied in form. In addition to the acicular structures, which are combined together in various ways to form multiradiate stars, there are various other kinds of firm parts, as, for example, the amphidiscs. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Gegenbaur, C. (Carl), 1826-1903; Bell, F. J. (Francis Jeffrey), 1855-1924; Lankester, E. Ray (Edwin Ray), Sir, 1847-1929. London, Macmillan and Co.
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