TUNICATA. 



253 



emits, at night, a most brilliant phosphorescent h'ght, 

 whence the derivation of the name by which it is 

 distinguished. Nothing can exceed the dazzling 

 splendour and brilliant colours exhibited by these 

 floating cylinders — colours passing rapidly from a 

 dazzling red to saffron, to orange, to green, and to 



W^mfk, 



/- 



Fig. 191.— ptrosoma. 



azure, and thus reflecting every ray into which the 

 prism divides the light, or which is exhibited by the 

 heavenly bow. 



If when walking on the sea-shore, about low- water 

 mark, we turn over large stones, or look under pro- 

 jecting eaves of rock, we are almost sure to see 

 translucent, jelly-like masses of various hues of orange, 

 purple, yellow, blue, grey, and green, sometimes 

 nearly uniform in tint, sometimes beautifully varie- 

 gated, and very frequently pencilled as if with stars 

 of gorgeous device, now encrusting the surface of 

 the rock, now depending from it in icicle-like pro- 

 jections. These are 



Compound Ascidians. A tangle or broad-leaved fucus 

 torn from its rocky bed, or gathered on the sands, 

 where the waves have cast it, will show us similar 

 bodies, mostly star-figured, investing its stalks, wind- 

 ing amongst its roots, or clothing with a glairy coat 

 the expanse of its foliated extremities. If we keep 

 some of these in a vessel of sea water, we find they 

 lie as apathetic as sponges, giving few symptoms 



