. A manual of zoology. Zoology. Fig. 299. Fig. Fig. Fig. 299.—Echinosphcrriles aiiranlium (from Zittel). 300.—FeiUremiles Jiorcalis (from Zittel). Lateral, oral, and aboral views. Siib Class IV. Blastoidca. Arms lacking; the mouth surrounded by five petaldike ambulacral areas. The group appears at end of Silurian and dies out with the carboniferous. Penlremiles (fig. 300). Class IV. Echinoidea (Sea Urchins). The structure of the sea urchins is best understood in the spherical forms (figs. 301, 303). Mouth and anus lie at opposite poles of the main axis, each opening immediately sur- rounded by
. A manual of zoology. Zoology. Fig. 299. Fig. Fig. Fig. 299.—Echinosphcrriles aiiranlium (from Zittel). 300.—FeiUremiles Jiorcalis (from Zittel). Lateral, oral, and aboral views. Siib Class IV. Blastoidca. Arms lacking; the mouth surrounded by five petaldike ambulacral areas. The group appears at end of Silurian and dies out with the carboniferous. Penlremiles (fig. 300). Class IV. Echinoidea (Sea Urchins). The structure of the sea urchins is best understood in the spherical forms (figs. 301, 303). Mouth and anus lie at opposite poles of the main axis, each opening immediately sur- rounded by areas covered by calcare- ous plates, the arrangement of which varies with the family. Around the anus is the periproct, around the mouth the peristome, the latter bearing sphas- ridia and in the Echinoids five pairs of interaml)ulacral gills. Between peristome and periproct the body wall {corona) is composed of calcareous plates, which, except in the Echinothu- rida;, are immovably united. Aside from the extinct Patechinoidea the plates are arranged in ten double meridional rows, two rows being always intimately associated together. Five of these double rows are ambulacral, the alternating five interam- bulacral. Both bear small hemispherical articular surfaces on which. Fig. 301.—Cceloplninis fioridanus* (after ). Aboral \'ie\v, the spines removed to show the ambula- cral (a) and (/)) interambulacral areas, ending respectively in the ocular and genital plates; in the centre the four plates of the 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 Hertwig, Richard, 1850-1937; Kingsley, J. S. (John Sterling), 1854-1929, ed. and tr. New York, H. Holt
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1912
