. Outlines of zoology. Zoology. 228 ECHINODERMA. mesodermic tissues (mesenchyme), and in consequence there is frequently a very complete skeleton. From the primi- tive gut of the larva, pouches grow out to form the usually spacious ccelofue and the characteristic water vas- cular systein. The branches of this system, together with the nerves, exhibit in most cases a typical five-rayed arra7igement. In development there is a marked disti?ic- tion between mesoblast derived from gut pouches, and mesen- chyme produced by immigrant amc&boid cells. There is usually a very striking circuitousness
. Outlines of zoology. Zoology. 228 ECHINODERMA. mesodermic tissues (mesenchyme), and in consequence there is frequently a very complete skeleton. From the primi- tive gut of the larva, pouches grow out to form the usually spacious ccelofue and the characteristic water vas- cular systein. The branches of this system, together with the nerves, exhibit in most cases a typical five-rayed arra7igement. In development there is a marked disti?ic- tion between mesoblast derived from gut pouches, and mesen- chyme produced by immigrant amc&boid cells. There is usually a very striking circuitousness or indirectness in development. The Echinoderms are all marine. By reason of their. P"lG. 74.—Pluteus larva with rudiment of adult. (After Johannes Muller.) du7-able skeletons, they are extremely well represented as fossils, yet this does not alter the fact that the group is well-defned, and shows no close relation to any other, whether in its livitig or extinct representatives. The average habit is sluggish, and this may be correlated with the constant development of lime in the tissues. This poiver of forming skeletal substance is indeed so deep-seated that lime may appear in almost any of the organs of the body. The diet is vegetarian (most sea urchins), carnivorous (starfishes), or consists of the organic particles found in sand. 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 Thomson, J. Arthur (John Arthur), 1861-1933; Newbigin, Marion I. (Marion Isabel), 1869-1934; Smith, Preserved, 1880-1941. fmo. New York, D. Appleton & Co.
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
