. Elements of comparative zoology. Zoology. 282 SYSTEMATIC ZOOLOGY. the lower surface; the vent is on the margin of the disc, or near the margin on the lower surface. It is interradial in position. Comparisons with forms like these, or better. A B a Fig. 96.—A, oral, and B, aboral surfaces of sand-dollar (Echinarachnius). a, vent; g, genital pores; i, ambulacral areas; m, madreporite; o, mouth. with Spatangoids (infra), show why the odd or unpaired ray of a starfish is called the anterior ray (see Laboratory work). In a few of the sand-cakes the margin of the disc is notched, while in others t
. Elements of comparative zoology. Zoology. 282 SYSTEMATIC ZOOLOGY. the lower surface; the vent is on the margin of the disc, or near the margin on the lower surface. It is interradial in position. Comparisons with forms like these, or better. A B a Fig. 96.—A, oral, and B, aboral surfaces of sand-dollar (Echinarachnius). a, vent; g, genital pores; i, ambulacral areas; m, madreporite; o, mouth. with Spatangoids (infra), show why the odd or unpaired ray of a starfish is called the anterior ray (see Laboratory work). In a few of the sand-cakes the margin of the disc is notched, while in others there may be perforations ex- tending through from upper to lower surface. Order III.—Spatangoids (Heart-urchins). In these the body, flat below, arched above, has a heart- shaped outline, and both mouth and vent are eccentric in position upon the lower surface. The ambulacra are all on the upper surface, but the anterior row is lacking. Class V.—HOLOTHURIDEA (Sea-cucumbers). The Holothurians are cylindrical Echinoderms, with mouth and vent at the ends of the body, and usually with the ambulacra scattered over the surface in such a way as to make the comparison with a cucumber most apt. Around. 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 Kingsley, J. S. (John Sterling), 1854-1929. New York, H. Holt and Company
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