. Elements of comparative zoology. Zoology. Phylum VI.—ECHINODERMA. The term Echinoderma means spiny skin, and both star- fishes and sea-urchins possess this peculiarity in a high degree. But besides this external characteristic there are many other features which dis- tinguish the group. In fact, there is scarcely a division in the whole animal kingdom more sharply marked off from other forms than this. In all the body is built on that radiate plan which is so prominent in starfish and urchin, and in all except a few starfish there are five rays, although in some the rays may subdivide. This
. Elements of comparative zoology. Zoology. Phylum VI.—ECHINODERMA. The term Echinoderma means spiny skin, and both star- fishes and sea-urchins possess this peculiarity in a high degree. But besides this external characteristic there are many other features which dis- tinguish the group. In fact, there is scarcely a division in the whole animal kingdom more sharply marked off from other forms than this. In all the body is built on that radiate plan which is so prominent in starfish and urchin, and in all except a few starfish there are five rays, although in some the rays may subdivide. This radiate condition affects not only the external surface, but may extend to every system as T J J J Fig. 90.—Larva of a starfish, en- well. And yet we may trace in larged. m, mouth; », vent, every form a bilaterality, and development shows that the bilateral condition is primitive, for the larvae (see fig. 90) clearly have the two sides alike, while the radial symmetry of the adult only appears later in the growth. It was this radial arrangement of parts which formerly led to the union of Echinoderma and Ccelenterata as a branch Radiata. a 273. 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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