. Elementary text-book of zoology. Zoology. 270 FIG. 210.—Calcareous bodies from the integument of Holothu- rians. a, calcareous wheels of Chirodotu; I, anchor with supporting plate of Synapta ; c, chair-like bodies ; d, plates of Holothuria impatient; e, hooks of Chirodotn. flattened out to form a more or less extended surface. The cylin- drical form is obtained by an elongation of the axis (Holothuroidea] (fig. 209), the round form by a shortening of the same and the penta- gonal disc by the latter process combined with a simultaneous elonga- tion of the radii. If the radii a
. Elementary text-book of zoology. Zoology. 270 FIG. 210.—Calcareous bodies from the integument of Holothu- rians. a, calcareous wheels of Chirodotu; I, anchor with supporting plate of Synapta ; c, chair-like bodies ; d, plates of Holothuria impatient; e, hooks of Chirodotn. flattened out to form a more or less extended surface. The cylin- drical form is obtained by an elongation of the axis (Holothuroidea] (fig. 209), the round form by a shortening of the same and the penta- gonal disc by the latter process combined with a simultaneous elonga- tion of the radii. If the radii are elongated till they are two or more times the length a b of the inter-radii, the form takes the shape of a star (Asteroidea), which may be either flat or arched. The arms of the star may be simple processes of the disc, and en- close a part of the body cavity (Stel- leridea, Star-fish), or they may be more independent moveable organs sharply marked off from the disc, and as a rule simple (Ophiuridw}, but sometimes branched (Euryalidce), or they may even bear simple jointed side twigs, the pinnuhe (Crinoidea). An important characteristic of the Echinodermata is the indura- tion by calca- reous deposits of the deeper layers of the A integument (dermal con- nective tis- sue), so as to give rise to a solid more or less moveable FIG. 211.—Skeletal plates of Astropecten HempncMii (after J. Miiller). moveable ar- DR, dorsal marginal ossicles ; VR, ventral marginal ossicles; Ap, T +li ambulacra! ossicles ; Jp, intermediate interambulacral ossicles ; Atlp, anterior adambulacral ossicles projecting into the mouth. leathery Holo- thuroidea (fig. 210) alone these skeletal structures are confined to isolated calcareous bodies, which are embedded in the integument, and have a definite form of latticed plates, wheels, or anchors. In these. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearan
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1884
