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Show 1867.] DR. j. E. G R A Y O N SPONGES. 531 Gaimard, one being a large conical siliceous sponge, and the other small branched calcareous one. And why are these sponges called Alcyonoid? They have no affinity to Alcyonium, which are true zoophytes. 3. HETEROTELLA. The tube short, rather irregular, conical, truncated, irregularly netted. Skeleton formed of thick bundles of very numerous slender spicules, placed in all directions, and forming an irregular network, similar to the network of the lid of Euplectella. HETEROTELLA CORBICULA. (Pl. XXVIII. fig. 2.) Alcyoncellum corbicula, Valenc. Mus. Paris; Bowerb. B. Sp. i. p. 176. Hab. Isle De Bourbon. I am indebted to Prof. Wyville Thompson for having first drawn my attention to the want of the regular longitudinal fascicule of spicules in these two genera, and also for most kindly presenting me with the photographs of the two sponges taken from the specimens in the Paris Museum, which are here copied. Fam. 2. ESPERIADEE. Skeleton composed of fusiform and linear spicules, interspersed with anchorate, bihamate, or birotulate spicules, which are either attached to the membranes or scattered in the sarcode, and form a defence to the sponge. The bihamate and anchorate spicula exist in large numbers on the surface of the interstitial membrane. The bihamate are fusiform spicula, bent at each end into the form of a hook, the curves being in the same plane or at right angles to each other, the tips are tapering and acute, or sometimes solid and club-shaped ; and rarely they are expanded into circular plates. The anchorate spicula always have their two terminations in the same position as those of the bow of an ordinary ship anchor. In some sponges they are tolerably uniform in shape and proportion; while in others they vary exceedingly, not only while in course of development, but even when in their adult condition. They glide so insensibly from one form into another that it is difficult to draw a distinction between them, even when there are a sufficient number of fully developed ones to exhibit the normal form. . In most cases, besides the large and fully developed anchorate spicules, there is found accompanying them a secondary series, which are very much smaller in size, and vary exceedingly both in symmetry and amount of development; they appear to be simply abortive developments of the larger and more perfect of the normal spicula. The anchorate spicula are gradually and progressively deve-veloped. They are to be found at both sides of the membranaceous skeleton, and are often very minute (see Bowerb. Phil. Trans. 1858, pp. 205, 300, 303). |