Medusae of the world . 8 loops are put into connection one with another by means of nerve tracts that runthrough the peronia. Thus the nervous system consists of an 8-lobed, star-shaped ring ofciliated ectodermal cells situated upon the exumbrella (see plate 55, figs. 1 and 2, n, n). In the adult medusa there are typically 24 marginal sense-organs, 3 in each octant of thebell, although occasionally there are as few as 2 or as many as 5 in an octant. Each sensoryclub is situated upon a small, hemispherical elevation of the bell-margin called the sensorycushion. The sensory cushion is formed fro
Medusae of the world . 8 loops are put into connection one with another by means of nerve tracts that runthrough the peronia. Thus the nervous system consists of an 8-lobed, star-shaped ring ofciliated ectodermal cells situated upon the exumbrella (see plate 55, figs. 1 and 2, n, n). In the adult medusa there are typically 24 marginal sense-organs, 3 in each octant of thebell, although occasionally there are as few as 2 or as many as 5 in an octant. Each sensoryclub is situated upon a small, hemispherical elevation of the bell-margin called the sensorycushion. The sensory cushion is formed from the cells of the nerve-cord, which at this placeare elongate and spindle-shaped and bear long delicate bristles. Centripetal to the sensorycushion, on the exumbrella surface of the bell, there is a small, elliptical, elevated ridge, theotoporpa, composed of a single layer of cube-shaped ectoderm-cells and containing a numberof nematocysts (see plate 55, figs. 1 and 2, 0). The sensory-club is rod-like and cylindrical. Fig. 305.—Larvae of Cunoclantha attached to mouth of Turritopsh drawing by Prof. W. K. Brooks. and is attached to the sensory cushion by means of a short, narrow neck (see plate 55, fig. 1).Each sensory-club contains two concretions that are situated within the entodermal core ofthe club. The proximal otolith is small and spherical, while the distal is large, flat, andcrystalline. The velum is more complex than in most hydromedusae, for it consists not only of a simpleannular membrane (see plate 55, figs. I and 2, v) that serves to partially close the opening ofthe bell-cavity; but in addition it extends upward as 8 A-shaped webs between the 8 loops ofthe nerve-cord (see plate 55, figs. 1 and 2 v), and thus it is that, morphologically speaking, themargin of the exumbrella is bounded by the nerve-cord and hence the true form of the disk isto be considered as an 8-rayed star, although the thin webs of the velum stretched between therays give it the
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectcnidari, bookyear1910
