Echinoderms of Connecticut (1912) Echinoderms of Connecticut echinodermsofcon00coew Year: 1912 88 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. arms, firmly fitted together. Thus the entire aboral surface of both disk and arms of the starfish can be represented in the sea-urchin only by the few plates of the periproct. Each ambulacral area ends near the periproct in a single plate called the ocular plate (Fig. 13), perforated by a pair of minute openings from which a tentacle protrudes, as at the end of the arm of the starfish. The interambulacral areas likewise terminate in single large pl
Echinoderms of Connecticut (1912) Echinoderms of Connecticut echinodermsofcon00coew Year: 1912 88 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. arms, firmly fitted together. Thus the entire aboral surface of both disk and arms of the starfish can be represented in the sea-urchin only by the few plates of the periproct. Each ambulacral area ends near the periproct in a single plate called the ocular plate (Fig. 13), perforated by a pair of minute openings from which a tentacle protrudes, as at the end of the arm of the starfish. The interambulacral areas likewise terminate in single large plates called the genital plates, because they bear the five openings of the genital glands (Plate XXV). One of these genital plates is larger than the others, and is per- forated by numerous minute pores which lead to the water- vascular system. This plate is therefore termed the madreporic plate (Fig. 13). M FIG. 13. Arbacia punctulata. Out- line of plates of aboral surface, showing the four plates of the peri- proct, surrounded by the five ocular and five genital plates at the ends of the ambulacral (R} and inter- ambulacral (/) zones, respectively; the genital plate marked M is the madre- poric plate; T, tubercles for attach- ment of spines; P, pores for the tube- feet. At the margin of the peristome are five pairs of much branched processes, having a respiratory function, and termed the dermal branchiae, or gills. Just inside the test at the border of the peristome, and resting upon the bases of the ambulacral areas, are five pairs of calcareous
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