NARCOMEDUSiE — CUNOCTANTHA. 



463 



contains many nematocysts and also deep-lying muscle fibers. Just beneath and centrifugal 

 to each tentacle-root is a thick pad of ectoderm-cells. This is the "peronium" of Haeckel 

 and it probably serves to support the tentacle that arises immediately above it. 8 loops of 

 the nerve-cord extend outward from the 8 peronia to the sense-organs upon the bell-margin. 

 These 8 loops are put into connection one with another by means of nerve tracts that run 

 through the peronia. Thus the nervous system consists of an 8-lobed, star-shaped ring of 

 ciliated 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 the 

 bell, although occasionally there are as few as 2 or as many as 5 in an octant. Each sensory 

 club is situated upon a small, hemispherical elevation of the bell-margin called the sensory 

 cushion. The sensory cushion is formed from the cells of the nerve-cord, which at this place 

 are elongate and spindle-shaped and bear long delicate bristles. Centripetal to the sensory 

 cushion, on the exumbrella surface of the bell, there is a small, elliptical, elevated ridge, the 

 otoporpa, composed of a single layer of cube-shaped ectoderm-cells and containing a number 

 of 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 nulricula. 

 From 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 of 

 the club. The proximal otolith is small and spherical, while the distal is large, flat, and 

 crystalline. 



The velum is more complex than in most hydromedusae, for it consists not only of a simple 

 annular membrane (see plate 55, figs. I and 2, v) that serves to partially close the opening of 

 the bell-cavity; but in addition it extends upward as 8 A-shaped webs between the 8 loops of 

 the nerve-cord (see plate 55, figs. 1 and 2 v'), and thus it is that, morphologically speaking, the 

 margin of the exumbrella is bounded by the nerve-cord and hence the true form of the disk is 

 to be considered as an 8-rayed star, although the thin webs of the velum stretched between the 

 rays give it the appearance of a hemispherical bell. 



Manubrium cone-shaped and there are 4 perradial, cruciform lips. 8 gastric sacs radiate 

 outward from the central stomach-cavity, each sac being found in a tentacular radius. There 

 are no radial-canals and no ring-canals in this species. The gonads are developed in the ecto- 

 derm of the subumbrella immediately beneath the 8 gastric sacs. 



The medusa is colorless with the exception of a delicate sage-green tinge of the entoderm 

 near the lips and occasionally in the tentacles. 



