. Outlines of zoology. Zoology. GENERAL SURVEY. 127 activity, for among them there is no sessile hydroid type. In our survey of the series, however, we must pass over these familiar types, and begin with the little fresh-water Hydra (Fig. 56), which is often to be found attached to the stems and leaves of water-plants. The structure here is extremely simple, but the simplicity is probably due to. Fig. 55.—Diagram of Coslenterate structure, endoderm darker throughout. 1. To left, shows longitudinal section of Hydra ; to right, of sea-anemone, g., gut; gl,, incipient gullet. -.:. To left, shows
. Outlines of zoology. Zoology. GENERAL SURVEY. 127 activity, for among them there is no sessile hydroid type. In our survey of the series, however, we must pass over these familiar types, and begin with the little fresh-water Hydra (Fig. 56), which is often to be found attached to the stems and leaves of water-plants. The structure here is extremely simple, but the simplicity is probably due to. Fig. 55.—Diagram of Coslenterate structure, endoderm darker throughout. 1. To left, shows longitudinal section of Hydra ; to right, of sea-anemone, g., gut; gl,, incipient gullet. -.:. To left, shows cross-section of Hydra; to right, of sea- anemone, in the region of the gullet. 3. To left, shows vertical section of Craspedote Medusoid (with velum) ; to right, of Acraspedote Medusa, with- out velum, g., gut; gL, gullet. Note anatomical correspondence of the polypoid and medu- soid forms. degeneration. In favourable conditions the polype may give off daughter buds, which remain for a time attached to the parent, and then separate as independent Hydra. The bud itself, before leaving the parent, may also bud, so that three generations are present. If we picture this process of gemmation, but with imperfect separation of the units, continued indefinitely, we can understand the formation of hydroid colonies, such as 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 Thomson, J. Arthur (John Arthur), 1861-1933. Edinburgh, Glasgow and London, H. Frowde and Hodder & Stoughton
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Keywords: ., bookauthorth, bookcentury1800, bookdecade1890, booksubjectzoology
