PHOSPHORESCENT COLONIES 299 



and pattern often strikes one very forcibly in the case of 

 creatures which live in dark pools, on the under-side of 

 yocks, or at considerable depth in the sea, where no eye 

 can ever see them. It is also striking in those cases 

 where the beautiful colour and design exists in some com- 

 pletely hidden or internal part of the plant or animal. It 

 ■is certainly not possible with our present knowledge to 

 ascribe the colour and beauty of many marine animals to 

 any utility or advantage to their owner. But this, of 

 <:ou'rse, is quite consistent with the fact — now most 

 thoroughly demonstrated — that in a great many cases the 

 ionce useless colour has been selected and preserved Jn 

 -certain- s.pots and shapes, and on various parts, so as to 

 be of 'great advantage to the animal or plant so coloured 

 in its relations to' surrounding . animals, whose eyes are 

 afifected, and whose actions are guided by the optical 

 impression^^ so produced* The same is true as to the 

 -phosphorescent light emitted in the> dark by- certain 

 animals and certain^ plants. In some instances we can show 

 its value- to the Hglit-maker ; butinmany other instances 

 •it appears to be a mere nonrsignificant by-product. 

 . Some of the composite growths formed by the budding 

 <kinds of Asddians are phosphorescent. We call a cluster 

 •of budded animals which remain in continuity with one 

 another "a colony." It is not perhaps a good' term, but 

 .it is the one in use. Such " colonies " or aggregates 

 formed by Ascidians are in some kinds irregular and 

 indefinite in shape ; in others they are definite in shape 

 as are the radiated star-like colonies of Botryllus. A 

 very curious kind of " colony," of definite shape, is 

 formed by the budding Ascidian known as ^'the 

 sea-candle," or " Pyrosoma." It is a hollow, pinkish- 

 «oloured translucent cylinder, three or four inches long as 

 commonly seen in the Mediterranean, but bigger species 

 (even four feet long) occur in tropical seas. At night, 



