. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 70 PORIFERA. yellow colour, somewhat translucent, pear- shaped, tapering more or less at their narrow end in different species ; their whole outer surface is covered with delicate projecting cilia, and when viewed through the micro- scope, in connection with the parent, we see that the rapid vibration of these cilia produces a distinct current in the water immediately around them, flowing always from their rounded free end towards their tapering fixed extremity, thus assisting the small granular bodies in producing the c
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 70 PORIFERA. yellow colour, somewhat translucent, pear- shaped, tapering more or less at their narrow end in different species ; their whole outer surface is covered with delicate projecting cilia, and when viewed through the micro- scope, in connection with the parent, we see that the rapid vibration of these cilia produces a distinct current in the water immediately around them, flowing always from their rounded free end towards their tapering fixed extremity, thus assisting the small granular bodies in producing the currents of the sponge during the period of their attachment to the body. They separate from the canals, and are propelled through the fecal orifices early in spring. None of these ova are seen in the sponge in summer, though we can detect no difference in the velocity of the currents at that period. For some time after they are propelled from the interior of the sponge, they swim about by means of the cilia on their surface, and exhibit all those extraordinary phenomena of spontaneous motion which Cavoliui, nearly half a century ago, discovered in the ova of the Gorgonia and Madrepore. They at length fix themselves, like the ova alluded to, on a spot favourable to their growth; they lose entirely their original form, and become a flat transparent circular film through which horny fibres shoot; they soon spread, anil assume a form similar to that of the ; * Gemmules.— Mr. Bowerbank has given the following description of the gemmules of Haliehondria Johnstonia. " The gemmules of this sponge are dispersed in great abundance throuuhout every part of its substance; they are of an oval form, the longest diameter being ^y-,th, and the shortest, the Tj^-th of an inch. Ttiey vary considerably in size, but the above are their average dimensions. When seen by direct light, with a power of 100 linear, they appear of the same colour as the surrounding fleshy matter ; but
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Keywords: ., bo, booksubjectanatomy, booksubjectphysiology, booksubjectzoology
