. A manual of zoology. Zoology. but elsewhere it is a double spiral. It ascends from the Biouth, turning once, and then, bending on itself, coils in the reverse direction to the anus (fig. 331). Usually the first portion of the canal is accom- panied by a siphon, an accessory tube opening into the main tube at either end. Excejit in the Sjjatangoids the mouth is surrounded by fire sharp-pointed calcareous plates, the teeth, fig. 332. — Aristotle's which in the Echinoids are supported by a 'Taurlfvsnvfa^i".^'^(A!t- complicated system of leyers, fulcra, and mus- d'?rto?'^™'^'aiveoii'; "
. A manual of zoology. Zoology. but elsewhere it is a double spiral. It ascends from the Biouth, turning once, and then, bending on itself, coils in the reverse direction to the anus (fig. 331). Usually the first portion of the canal is accom- panied by a siphon, an accessory tube opening into the main tube at either end. Excejit in the Sjjatangoids the mouth is surrounded by fire sharp-pointed calcareous plates, the teeth, fig. 332. — Aristotle's which in the Echinoids are supported by a 'Taurlfvsnvfa^i".^'^(A!t- complicated system of leyers, fulcra, and mus- d'?rto?'^™'^'aiveoii'; ""X cles, the 'lantern of Aristotle' (fig. 332). *'^''''''' The ring canal and the ring of the blood system lie on the lantern, the stone canal and ovoid gland ('heart') extending upwards from them (fig. 330). The blood-vascular ring gives off two blood-vessels which run along the alimentary canal, while from the ring canal arise five ambulacral or radial canals which run on. Fig. 333.—Oral {A^ and aboral (S) surfaces of the sand dollar. Echinaracltnius pai-ma. a, anus ; y, genital pores ; i, ambulacral areas ; vt, madreijorite ; o, mouth. the inner side of the test accompanied by nerves which radiate from a nerve ring. The gonads are five (rarely four or two) uiqtaired organs in the aboral half of the test, opening through the genital jilates, that is, interradially as in the starfish. Order I. Paleeechinoidea. Paleozoic forms with five ambulacral areas, the interambulaorul areas containiug more tlian two rows of plates. Meloidtts. Order II. Cidaridea (Regulares). Ambulacral areas band-like, body more or less spherical, mouth and anus polar. Here belong the common urchins, represented on our coasts by Toxopneustes* StrongyTocentrotus* Arhacia* Calopleurus* (flg. 328).. 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
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectzoology, bookyear1902
