. The wonder of life. Biology; Natural history; Zoology. 69.—^Minute trans- parent free-swimming larva of a sea-cucum- ber or Holothurian, showing transverse bands of cilia (c) and peculiar protrud- ing ' arms ' (a). tubse,' about an eightli of an inch in height, with a mouth, gullet, and tentacles. In ordinary conditions this sedentary stage grows larger, and displays a series of transverse annular con- strictions, becoming hke a minia- ture pile of saucers—the strobila stage. Each disc or saucer is separated off in turn as a free- swimming young jeUy-fish (or Pig. 69.—Minute trans- Bphyra),
. The wonder of life. Biology; Natural history; Zoology. 69.—^Minute trans- parent free-swimming larva of a sea-cucum- ber or Holothurian, showing transverse bands of cilia (c) and peculiar protrud- ing ' arms ' (a). tubse,' about an eightli of an inch in height, with a mouth, gullet, and tentacles. In ordinary conditions this sedentary stage grows larger, and displays a series of transverse annular con- strictions, becoming hke a minia- ture pile of saucers—the strobila stage. Each disc or saucer is separated off in turn as a free- swimming young jeUy-fish (or Pig. 69.—Minute trans- Bphyra), which feeds on micro- scopic organisms, grows rapidly, undergoes certain structural changes, and becomes a sexual jelly-fish. Thus we find that a characteristically free and active animal, the jelly-fish, includes in its life-history a fixed and vegetative polyp-stage—alternation of generations again (see Fig. 72). Echinodertns. — The newly- hatched larvse of sea-urchins, sea- cucumbers, starfishes, and brittle stars are diffusely ciliated two- layered thimble-hke sacs—in fact, not very remarkable gastrulse. But they soon become quaintly transformed by the outgrowth of processes and the formation of special bands of cilia into extra- ordinarily shaped larvae, adapted for open sea hfe. In sea-urchins, for instance, the quaint larva, known as a Pluteus, is often. JFia. 70, Minute trans- parent free-swimming larva of a sea-oucuni- ber or Holothurian, showing peculiar pro- truding ' arms' (a) and calcareous plates (CP).. 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 Thompson, John Arthur, Sir, 1861-1933. London, A. Melrose, Ltd
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Keywords: ., bookcentury1900, booksubjectnaturalhistory, booksubjectzoology
