. The Cambridge natural history. Zoology. ECHINUS—PEDICELLARIAE 509 animals, which would otherwise settle on the delicate exposed ectoderm of the Sea-urchin. The gemmiform pedicellariae are brought into action when a more serious danger threatens the Sea-urchin, such as an attack •of a Starfish. The corrosive chemical influence, which it can be proved exudes not only from the stomach but even from the tube-feet of the Starfish, causes the gemmiform pedicellariae to approach and open widely. When the foe approaches so closely as to touch the sense-organs (Fig. 225, B, s) situated on the inner.
. The Cambridge natural history. Zoology. ECHINUS—PEDICELLARIAE 509 animals, which would otherwise settle on the delicate exposed ectoderm of the Sea-urchin. The gemmiform pedicellariae are brought into action when a more serious danger threatens the Sea-urchin, such as an attack •of a Starfish. The corrosive chemical influence, which it can be proved exudes not only from the stomach but even from the tube-feet of the Starfish, causes the gemmiform pedicellariae to approach and open widely. When the foe approaches so closely as to touch the sense-organs (Fig. 225, B, s) situated on the inner. Fig. 225.—The pedicellariae of Echinus acutus, drawn from a living specimen. A, gemmiform pedicellaria, closed. B, gemmiform pedicellaria, open ; g, poison gland ; s, sense-organ, X 3. C, tridactyle pedicellaria, x 6. D, ophicephalous pedicellaria, X 9. E, trifoliate pedicellaria, x 12 ; a (in all figures), axial rod of the stalk. (After Uexktill.) side of the valves of these pedicellariae, the blades close violently, wounding the aggressor and causing its juice to exude, thus producing a renewed and severe chemical stimulation which irritates the poison glands and causes the poison to exude. The virulence of the poison may be gauged from the fact that the bite of a single gemmiform pedicellaria caused a frog's heart to stop beating. Prouho^ has described a combat between a Sea-urchin and a Starfish. When the latter approached, the spines of the Sea- 1 " Du rOle des p^dioellaires gemmiformes des Oursins," Compt. Rend. Acad, de Paris, cxi. 1890, pp. 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 Harmer, S. F. (Sidney Frederic), Sir, 1862- ed; Shipley, A. E. (Arthur Everett), Sir, 1861-1927. ed. [London, Macmillan and Co. , Limited; New York, The Macmillan Company
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
