RADIATA. 29 
‘London, 1848, pl. 1, fig. 1). The same structure occurs in Berenice (Cuv. 
Régne An. Zooph., pl. 53, fig. 1"). In the covered-eyed group, the branches 
after extending about two thirds the distance towards the edge anasto- 
mose around the margin in a broad and close vascular net-work (beautifully 
exhibited in Milne Edwards’ figure of Rhizostoma, R. An. pl. 50). 
The position of the generative system is variable in this class. In general 
both sexes seem to be united in the same individual. 
When the ocelli are present, the sense of sight is probably sufficient to 
enable the animal to distinguish between light and darkness, and the sense 
of hearing may also be present. Their food is furnished by small marine 
animals, among which the crustacea fill a prominent place. The sense of 
feeling is probably most developed in the palpi, the tentacles, and the arms, 
arising from the centre, and surrounding the mouth or pedicle. 
The stinging quality is not universal in the Medusa, being apparently 
confined to a few of the higher forms. Bathers sometimes suffer severely 
by coming in contact with the larger species, whose long tentacles and arms 
are sometimes entangled around the limbs, and cast off by the animal, 
leaving the sufferer to disengage himself from these unwelcome appendages 
at his leisure. The stinging property is supposed to be confined to an 
external coat of mucus, which the animal can cast off. 
The luminousuess of the sea is due chiefly to multitudes of acalephee. 
“At one time, the evening serene and delightful, a pleasant breeze just 
filling the sails, and the bow of the vessel throwing the water to each side, 
as it gracefully parts the yielding waves, all round the ship, far as the eye 
can reach, may be seen innumerable bright spots of light rising to the 
surface, and again disappearing, like a host of small stars dancing and 
sparkling on the bosom of the sea. At another time, the night dark and 
lowering, a fresh breeze urging the ship rapidly onwards through her 
pathless track, upon looking over the stern, in addition to the smaller specks 
just now mentioned, large globes of living fire may be seen dancing in the 
smooth water in the wake of the rudder; now, at a great depth, shining 
through the water, then rising rapidly to the surface, they may be seen, as 
they reach the top of the wave, flashing a bright spark of light, sufficient 
almost to dazzle the eyes of the beholder; and now, again, they may be 
traced floating majestically along, till they gradually disappear in the 
darkness of the water in the distance. At other times, again, when light 
rain is falling, or, perhaps, previously to the rain coming on, when a light 
nimbose cloud is overspreading the sky, upon the water being agitated by 
the ship passing through it, a beautiful general luminousness is diffused all 
round, bright enough to illuminate the whole ship’s side, and the lower large 
sails; and it is no unusual occurrence to have the appearance so bright, 
that a person with little difficulty, and near the surface of the water, might 
be enabled to read a book by its aid. . . It is in warmer regions and 
more southerly latitudes that this phenomenon attains its greatest degree 
of brilliancy and beauty.”— W. Baird, On the Luiminousness of the Sea, 
with figures. Mag. Nat. Hist. 1830, vol. 3, p. 808; vol. 4, p. 500. See 
also vol. 6, pp. 314-319. 
Luminous acalephz occur upon the coast of the United States, and they 
may be observed on a night passage in a steamboat in Long Island Sound. 
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