RADI ATA. 29 



London, 1S4:S^ pi. 1,^</. 1). The same structure occurs in Berenice (Cuv. 

 Regne An. Zooph., j9^. 53, ß^. 1"). In the covered-eyed group, the branches 

 after extendino; 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. 2^1. 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 suflicient 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 Medusae, 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 luminousness of the sea is due chiefly to multitudes of acalephoe, 



" 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 througli her 

 pathless" track, upon looking o"vei"the stern, in addition to tlie 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, suflicient 

 almost to dazzle the eyes of the beholder ; and now, again, they may be 

 traced floating majestically along, tnll 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 diflused 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 beautv." — W. Baird, On tlie Luminousness of tJie Sea, 

 with figures. Mag. Wat. Hist. 1830, vol. 3, p. 308 ; vol. 4, p. 500. See 

 also vol. 6, pp. 314-319. 



Luminous acalephaj occur upon the coast of the United States, and they 

 may be observed on a night passage in a steamboat in Long Island Sound. 



233 



