Page:Natural History, Mollusca.djvu/325

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ASCIDIAN MOLLUSKS.

organically possessing a compound life. Through these last-named the transition is easy and natural to the lowest forms of animal life, the Polypes; for the Class of animals denominated Bryozoa or Polyzoa, which form the exquisite aggregations of calcareous cells known as Sea-mats (Flustra), and their allies, are truly Ascidians in their structure, with their entering orifice surrounded by a radiated circle of ciliated tentacles.


Family Ascidiadæ.

Whoever has turned over stones at the extreme verge of low-water (and there is no student of marine natural history who has not) is familiar with uncouth pellucid bodies adhering to their under surfaces, that resemble bags, of a substance somewhat between leather and jelly. The dredger, however, is far more familiar with them, for scarcely can any part of the bottom of the sea be raked without an abundance of these curious creatures being brought up, varying much in size and colour. Some are sufficiently rude and uncouth, coarse and rough in texture, and dingy in hue; others are attractive, often of brilliant colours, of a semi-transparent clearness, resembling strange pellucid fruits, or masses of ice. They are always found adherent, either by the base of the sac or by its side, to foreign bodies as stones, shells, and sea-weeds, and thus not only are they deprived of locomotion, but almost of all appearance of vitality, for no movement is perceptible in them externally, except the periodical opening and closing of the two orifices which give admission and exit to the currents of water for respiration and food.