. A manual of zoology for the use of students : with a general introduction on the principles of zoology . Zoology. annuloida: echinodekmata. 151 the rays. The larva is venniform, and has no pseud embryonic skeleton. The skeleton of the Asteroidea is. composed of a vast number of small calcareous plates, or ossicula, united together by the coriaceous perisome, so as to form a species of chain-armour. Besides these, the integument is abundantly supplied with spines, tubercles, and " ; Lastly, the radiating ambulacral vessels run underneath a species of intern^ skele- ton
. A manual of zoology for the use of students : with a general introduction on the principles of zoology . Zoology. annuloida: echinodekmata. 151 the rays. The larva is venniform, and has no pseud embryonic skeleton. The skeleton of the Asteroidea is. composed of a vast number of small calcareous plates, or ossicula, united together by the coriaceous perisome, so as to form a species of chain-armour. Besides these, the integument is abundantly supplied with spines, tubercles, and " ; Lastly, the radiating ambulacral vessels run underneath a species of intern^ skele- ton, occupying the axis of each arm, and-composed of a great number of bilateral " vertebral ossicles " or calcareous plates, which are movably articulated to one another, and are provided with special muscles by which they can be brought together or drawn apart The upper surface of a star-fish corresponds to. Fig. 42.—Crihella oculata. (After Forbes.) the combined ihter-ambulacral areas of an Echinus, and ex- hibits the aperture of the anus (when present), and the " mad- reporiform tubercle," which is situated near the angle between two rays. The inferior or ventral surface corresponds to the ambulacral areas of an Echinus, and exhibits the mouth and ambulacral grooves. The mouth is central in position, and is not provided with teeth; it leads, by a short gullet, into a large stomach, from which a pair of sacculated diverticula are prolonged into each ray. A distinct intestine and anus may, or may not, be pre- sent ; but the anus is sometimes wanting (in the genera, Astro- pecten, Ctenodiscus, and Luidid). The aftibulacral system is essentially the same as in the Echinoidea, and is connected with the exterior by means of the. 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 Nicholson, Henr
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Keywords: ., bookauthorni, bookcentury1800, bookdecade1870, booksubjectzoology
