ACTINOZOA. 213 



excited, it flashes up more intensely, and when 

 suddenly immersed into alcohol, throws out the 

 most brilliant light." Experiments performed 

 on our own British Pennatula phosphorea led 

 Professor E. Forbes to the conclusion that this 

 species is " phosphorescent only when irritated by 

 touch " ; but it seems safer to infer that the light, 

 itself the index of an energetic display of vital 

 power, is only evoked in answer to proper stimuli, 

 which may very well be expected to occur more 

 appropriately in nature, though, doubtless, under 

 a form less clumsy, than in the exaggerated con- 

 ditions of an experiment. Forbes also showed 

 that the phosphorescence, when thus excited ])y 

 shock, sparkles onward from the portion struck in 

 an upward or distal direction, still, however, con- 

 tinuing to be emitted from the point of prime 

 contact. The vividness of the luminosity appears 

 to bear a direct ratio to the living energy of the 

 animal. Such are the chief conditions of its 

 manifestation, but the true cause of this pheno- 

 menon, as of vital phosphorescence in general, 

 still remains almost wholly unknown. 



Four families of Alcyonaria may be defined : 



Order ALCYONAEIA. 



Family i. Alcyonid^. 



Corallurn sclerodermic, in general spicular, 

 without true calcareous thecae. Cosnosarcfixed. 



Family 2. TuBiPORiOiE. 



Corallujn consisting of a number of distinct 

 corallites, destitute of septa, their thecge united 

 externally by horizontal plates, arranged at 

 distant intervals. Coenosarc fixed. 



P 3 



