Elements of comparative anatomy (1878) Elements of comparative anatomy elementsofcompar00gege Year: 1878 20G COMPAEATIVE ANATOMY. Fig. 104. Pedicellaria! ofEcliiuus saxa- t i 1 i s. A A Pedicel- laria with its pincer- arms open ; B With them closed (after Erdl). ambulacral canal, and so point to an affinity with this skeleton. The skeleton of the masticatory apparatus in the Echino'ida and Clypeastrida is to be regarded as an independent development; it surrounds the commencement of the enteron, and consists of a number of calcareous blocks connected together like a scaffold. Spine-like pr
Elements of comparative anatomy (1878) Elements of comparative anatomy elementsofcompar00gege Year: 1878 20G COMPAEATIVE ANATOMY. Fig. 104. Pedicellaria! ofEcliiuus saxa- t i 1 i s. A A Pedicel- laria with its pincer- arms open ; B With them closed (after Erdl). ambulacral canal, and so point to an affinity with this skeleton. The skeleton of the masticatory apparatus in the Echino'ida and Clypeastrida is to be regarded as an independent development; it surrounds the commencement of the enteron, and consists of a number of calcareous blocks connected together like a scaffold. Spine-like processes are connected with the integument in the Echino'ida, as well as in the Asteroi'da, but they are more independent owing to their power of movement. They are articulated to protuber- ances of the calcareous plates, and are provided with a special system of muscles. The spines vary greatly in form and size ; sometimes they are as fine as hairs (Spatangidas); sometimes club-like structures (Acrocladia); sometimes they are long rods (Cidaris). The Pedicellariaa are also dermal organs of a peculiar character, which are found in the Asteroi'da, as well as in the Echino'ida. They consist of a stalk-like muscular process of the integument, which is supported at its end by a fine calcareous skeleton; it terminates in two or three pincer-like valves, which are movable on one another. These too are provided with a calcareous skeleton. In the Echino'ida the three-valved, and in the Asterida the two-valved forms predominate. Brisinga resembles the Asterida in this point. They arc scattered over the whole body; but in the Asterida they are principally found at the base of the spicules, and in the Echino'ida in the perisome around the mouth. These bodies may be regarded as spines modified in such a way that the incompletely calcified stalk of the pedicellaria corresponds to the stalk of the paxilla of the Asterida; the tuft of spinules on the latter being represented by the arms of the
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