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Quarterly Journal of Microscopical Science, Vol s3-102, 531-542, Copyright © 1961 by Company of Biologists

Properties of the Wall of Leucosolenia variabilis

I. The Skeletal Layer

W. CLIFFORD JONES 1

1 Department of Zoology, University College of North Wales, Bangor

Pieces of the wall were photographed while being stretched by a pair of light weights. The extension took place slowly and removal of the weights was not followed by appreciable elastic recoil. On the photographic records, however, slow recoil could be detected in places. The slowness of both extension and recoil are attributed to the mesogloeal matrix and its embedded spicules; the changes in shape necessitated plastic deformation of the matrix.

Changes in the arrangement of the spicules on the photographic records confirm that the matrix underwent plastic deformation, while firmly embedding the spicules. Also the matrix yielded in places, whereupon the epithelia in the vicinity became greatly stretched and recoil occurred on each side of the region concerned.

In some parts of the oscular edge the epithelia contracted and caused the spicules to become crowded together.

Small developing spicules often underwent rotation on the stretching pieces and in some cases the rotation exceeded 180°. While their founder calcoblasts were probably attached to the epithelium which joins the gastral ends of the pores together, the attachment cannot be regarded as permanent, since the rotation, and also spicule growth, require that the calcoblasts at the tips of the rays should be able to move over the surface of the epithelium. The rotation of some developing spicules was associated with a displacement relative to the mesogloeal matrix.

The photographed pieces could not be held for a sufficient time (over 20 h) for new patterns of orientation to be shown by the developing spicules, but on one unphotographed piece this was possible, and small spicules oriented in the opposite direction to the fully formed ones were found near the basal edge, just behind a region of spicule crowding at the edge itself.

The relevance of these observations to the mechanism of spicule orientation is briefly considered.






© The Company of Biologists Ltd 1961