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Show 28 DR. J. S. BOWERBANK ON HYALONEMA MIRABILE. [Jan. 10, ingly long aud comparatively few in number, and do not appear to be connected with the parietes of the organ ; while in Ciocalypta they are short and very numerous, and the axis is connected with the'sides of the cloaca. Thus, when we consider the spiral column and its delapidated dermal coating alone, as it is usually received from the Japanese, and without reference to the basal mass of sponge belonging to it in its natural condition, the species presents an exceedingly anomalous appearance; but when the entire animal is considered and compared with other sponges, the anomaly is dissipated, and it is seen to present very few anatomical and no physiological differences from a numerous series of well-known sponges. The dermal membrane of the basal portion of the' sponge in the British Museum has been nearly entirely destroyed, a few fragments only remaining in situ. It appears to have been thin, pellucid, and aspiculous, or with a few adventitious spicula attached to its surface. The numerous inflato-fusiformi-acerate external defensive spicula do not appear to perforate it in the natural condition of the sponge ; but the fragments of the membrane in situ were so small as scarcely to allow of speaking on this point decisively. The spicula of the skeleton are exceedingly variable in length and proportions, and. are often curved to a very considerable extent, or they are flexuous ; and amongst them there are occasionally found exceedingly large fusiformi-acerate spicula, the diameters of which are equal to that of six or seven of the ordinary spicula of the skeleton ; and at irregular intervals we find very large attenuato-rect-angulated hexradiate spicula, which probably served to connect the flakes or layers of the skeleton together (Pl. V. fig. 1 a). I found hut one small group of the external defensive spicula in situ; but this was exceedingly characteristic. The spicula (Pl. V. fig. 5) are very numerous and closely packed together in parallel lines, and they are apparently projected about half their length beyond the outer surface of the mass of the skeleton. These spicula represent the shaft of an attenuated rectangulated hexradiate spiculum, with the inflation at about the middle of the shaft, whence the four lateral radii of that form of spiculum would spring. But the striking peculiarity of their structure is the mode of their adaptation as external defensive spicula, by the projection from all parts of the distal half of the shaft of numerous small spines at ascending angles of about 20 degrees to the long axis of the spiculum ; while on the proximal half of the spiculum there is rarely even the rudiment of a spine to be detected. The central inflation of the spiculum is usually projected beyond the external surface of the mass of the skeleton. A secondary series of defensive spicula are projected from the surface of the mass of the skeleton, and these consist of spiculated cruciform spicula as-cendingly and entirely spinous. They are also exceedingly numerous, their cruciform bases all being nearly in the same plane, and their spicular radii nearly parallel to each other, the apices reachino* to about the central inflations cf the large external defensive spicula^ These secondary external defensive spicula are in reality the internal defensive spicula of the sponge. They are perfectly novel in their |
