Studies of the Blood and Tests of Some Australian Ascidians. III. The Formation of the Test of Pyura stolonifera (Heller)

Abstract

Certain blood cells, termed ferrocytes, produce fibres when cytolysed. Similar fibres may be produced by these corpuscles when kept in "hanging drop" preparations. In both cases histological and histochemical examination shows that the fibres are identical with those present in the test.

Under normal conditions ferrocytes migrate across the walls of bloodvessels and enter the test substance. After moving about for a time amongst the fibrillar matrix already deposited, they produce fibres by one of three methods :

(i) A cytoplasmic centre, from which fibres subsequently arise, may be isolated from the main corpuscular mass.

(ii) Fibres may arise directly from the surface of the ferrocyte.

(iii) Fibres may arise from material secreted by the ferrocyte into its immediate vicinity.

In many respects the process of test fibre formation resembles the production of vertebrate connective tissue fibres from fibroblasts.

During regeneration of the test, ferrocytes migrate straight to the test sea-water interface and there produce fibres, seemingly as a direct result of the release of fibre-producing intraglobular material on cytolysis. The probable mode of formation of the tough outer test is also discussed.