Pearls & parasites / by Arthur E. Shipley.

  • Arthur Shipley
Date:
1908
Catalogue details

Licence: In copyright

Credit: Pearls & parasites / by Arthur E. Shipley. Source: Wellcome Collection.

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    ficient in lime, and are fibrous or cartilaginous in composition. Their scales, too, are thin and mem- branous, their skin soft and velvety. The shells of deep-sea molluscs are as thin and translucent as tissue-paper; and the same is true of some brachio- pods. The test of the echinoderms is often soft, and the armour of the Crustacea is merely chitinous, unhardened by deposits of lime. Calcareous sponges are altogether unknown in the depths. This inability to form a hard skeleton—curiously enough this does not apply to corals—is not due to any want of cal- careous salts in the bottom waters. It is known that calcium sulphate, from which animals secrete their calcium carbonate, exists in abundance; but those animals which dwell on the calcareous globigerina ooze are as soft and yielding as those which have their home on the siliceous radiolarian deposits. Animals which form a skeleton of silex do not suffer from the same inability; in fact, the deep-sea radio- lanans often have remarkably stout skeletons, whilst the wonderful siliceous skeletons of the hexactinellid sponges are amongst the most beautiful objects brought up from the depths. The second peculiarity, for which there seems no adequate reason, is the reduction and diminution in size of the respiratory organs. Amongst the Crus- tacea, the ascidians, and the fishes this is especially marked. The gill laminae are reduced in number and in size; and the evidence all points to the view that this simplification is not primitive but acquired, being brought about in some way by the peculiar conditions of life at great depths. When the first attempts were made to explore the bed of the ocean, it was hoped that the sea would give up many an old-world form; that animals, known to us only as fossils, might be found lurking in the abysmal recesses of the deep ; and that man}?- a missing
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