. Text-book of zoology for junior students. Zoology. IOl INVEUTEBHATE ANIMALS. The digestive system in Echinns consists of a mouth armed with a curious apparatus of calcareous teeth, wliich opens into a gullet, which ill turn conducts to a long intestinal tube. The teeth form a pyramidal structure known as "Aristotle's lantern"; but many ,Sea - urchins are without teeth. The long and convoluteil intestine is attached to the intei'ior of the shell by a delicate membrane or " mesentery," and terminates in a dis- tinct vent. The surface of the mesentery, as well as t
. Text-book of zoology for junior students. Zoology. IOl INVEUTEBHATE ANIMALS. The digestive system in Echinns consists of a mouth armed with a curious apparatus of calcareous teeth, wliich opens into a gullet, which ill turn conducts to a long intestinal tube. The teeth form a pyramidal structure known as "Aristotle's lantern"; but many ,Sea - urchins are without teeth. The long and convoluteil intestine is attached to the intei'ior of the shell by a delicate membrane or " mesentery," and terminates in a dis- tinct vent. The surface of the mesentery, as well as that of the lining membrane of the shell, is richly ciliated, and thus serves to distribute the fluid which iills tlie cavity of the Ixidy, and. m. — Chluris papilUilu. (AftiT Goss.'.) which corresiionds with the blood, to all parts of the body. It is doubtful if any true blood-system is present, but there is present a .system of tubes, of which the principal portion is a long fusi- form vessel running parallel with the saud-canal, and which have been legarded as blood-vessels. The nervous .system consists of a gangliated ccjrd jilaced round the gullet, and sending five radiating branches along the anibulacral areas. The two sexes are distinct, but in both the rejiroductive organs are in the form of five membranous sacs placed in a ra<liating manner in the interamlmlacral areas, and opening at the genital ]ilates. The majority of the Sea-urchins iire found at moderate depths in the sea, especially in the neighbourhood of oyster-banks. Others spend their existence liiiiied in the sand ; and one species excavates holes for itself in the solid rock, ajiparently by some mechanical 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, Henry Alleyne, 1844-1899. New York, American Book C
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1885
