The Origin of Sponge-Spicules

Abstract

IN the preliminary account by my friend Prof. Dendy (NATURE, February 7, p. 190) it is difficult to see evidence for the independent organic life of his “scleroplastids”. There is nothing to prove this, hypothesis in the observation that the first rudiment of the spicule in Stelletta is a skeleton-crystal on the tetrahedral system, afterwards overlaid (as we have long known in the tetracrepid desma of Lithistida) with siliceous deposit in amorphous aggregation. Obviously twinning and repetition of branches (also long known) are not arguments against the crystalline character of form in spicules. In 1898 I pointed out certain resemblances to the relations between a symbiotic organism and its host in the relations between a crystal, utilised as a spicule, and the sponge which has secreted it (Proc. Roy. Soc., vol. 64, p. 71). These resemblances seem to have misled Prof. Dendy to his new theory, but he adduces no facts which give evidence for separate organic life in the spicule, or impeach the evidence for its crystalline structure.