RADIATA. 29 



London, 181-8, ^_;Z. l^fig. 1). The same structure occurs i i Berenice (Cuv. 

 Kegne An. Zooph.,/>^. 53, Jig. 1"). In the coverecl-eyecl groujj, the branches 

 after extending about two thirds the distance towards the edge anasto- 

 mose around the margin in a broad and ch:)se vascuhir net work (beautifully 

 exhibited in Milne Edwards' figure of Rhizostoma, Ti. 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, tlie 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 sufi'er severely 

 by coming in contact with the larger species, whose long tentacles and arms 

 are sometimes entangled around the limbs, and cast oif 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 oft'. 



The luminousness of the sea is due chiefly to multitudes of acalephro. 



"At one time, the evening serene and delightful, a pleasant breeze just 

 filling the sails, and the bo^^"of the vessel throwing the water to each side, 

 as it gracefully parts the yieWing waves, all round the ship, tar as tlie eye 

 can reach, may be seen innumerable bright spots of light risinj^ 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 o'ver the stern, in addition to the snuiller 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 niay 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, 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 difiused all 

 round, bright enough to illuminate the whole ship's side, and the lower large 

 sails ; and it is no imusual occurrence to have the appearance so bright, 

 that a person with little difiiculty, 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."— IF. Baird, On the Luminousness of tlie Sea, 

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

 also vol. 6, pp. 314-319. 



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

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



933 



