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 ...
PROF. DENDY'S memoir (in Acta Zoologica, 1921, pp. 95-152, 50 figures) on the evolution of the tetraxonid sponge-spicule will appeal equally to those interested in problems of evolution or in ...
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