150 ANTHOZOA ASTEROIDA. 



Although it has not been proved that all Hydroid zoo- 

 phytes are phosphorescent, yet they appear to be more 

 generally so than the Asteroids, in which the power to produce 

 light is limited, so far as is yet known, to one family. This 

 is the Pennatulidse, every member of which is luminous at will 

 perhaps, although they light up their tiny lamps apparently 

 only when under the influence of some painful irritation ; * 

 Will-o-the-wisps of the sea, put out to frighten feeble assail- 

 ants. I have repeatedly kept living specimens for several 

 days in sea- water, and have observed them at all hours, with- 

 out once detecting them in a voluntary emission of the flame. 

 From some experiments made on Pennatula phosphorea. Pro- 

 fessor Edward Forbes draws the following inferences : — "1st, 

 The polype is phosphorescent only when irritated by touch ; 

 2d, The phosphorescence appears at the place touched, 

 whether it be the stalk or the polypiferous part, and proceeds 

 from thence in an undulating wave to the extremity of the 

 polypiferous portion, and never in the other direction ; 3d, If 

 the centre of the polypiferous portion be touched, only those 

 polypes above the touched part give out light ; and if the ex- 

 treme polypiferous pinna be touched, it alone of the whole ani- 

 mal exhibits the phenomenon of phosphorescence; 4th, The light 

 is emitted for a longer time from the point of injury or pres- 

 sure than from the other luminous parts ; 5th, Sparks of light 

 are sometimes sent out by the animal when pressed — these 

 are found to arise from luminous matter investing ejected 

 spicula." — Subsequent experiments did not always give the 

 same results, for, as Mr. Forbes writes me, " unless the ani- 

 mal be in the highest state of vivacity, the stalk shews no 

 phosphorescence, and the light of the feathered portion only 

 runs a short way, but always towards the upper extremity. 

 When plunged in fresh water, the Pennatula scatters sparks 

 about in all directions, — a most beautiful sight ; — but when 

 plunged in spirits, it does not do so, but remains phosphores- 

 cent for some time, the light dying gradually away, and last 



* Since the pages on the phosphorescence of the Hydroid zoophytes were printed 

 off, I have received a letter from Professor E. Forbes, in which he says, — " The 

 finest way of observing the phosphorescence of the Hydroids is to cast them into 

 f'rcali water in the dark. The vesicles, when full and fresh, give out the most vivid 

 light. This I have observed in several species of Sertularia." 



