CONTRACTILITY AND PHOSPHORESCENCE. 185 



of different chemical substances — alkaline, acid, and neutral — 

 upon Noctiluca have been investigated, the general result being 

 that any agent wJiatsoever capable of causing the protoplasmic 

 substance to contract zuas efficacious to precisely the same degree 

 and at the same time in producing phosphorescence. An isolated 

 shock caused during the daytime a violent but momentary con- 

 traction ; at night it gave rise to a bright but transient exhibi- 

 tion of light. 



Under the influence of continued or too violent irritation, 

 the whole substance of the body is seen in daytime to contract 

 to such an extent as to become free from the external envelope, 

 and gradually become disorganized or lose its vital properties. 

 At night the same operation leads to a continual phosphores- 

 cence, apparently pervading the whole animal. The steady 

 and permanent brilliancy always denotes approaching dissolu- 

 tion. Thus contraction and phosphorescence are invariably 

 met side by side, and, as it were, hand in hand. The contrac- 

 tion of the protoplasm may be either partial or general ; it may 

 manifest itself in different places at the same time, and so also 

 with the luminosity. The important point to bear in mind in 

 this connection is Ouatrefages' discovery that tJie luminous 

 area of the Noctiluca is composed of an enormous number of 

 luminous points. 



Examined with a power of twenty or thirty diameters, the 

 illuminated portion is uniformly bright. With sixty diameters, 

 a number of small but brilliant scintillations become visible, 

 and these come and go with the rapidity of lightning. An 

 enlargement of one hundred and fifty diameters reveals the 

 true character of the phenomenon. It then becomes obvious 

 that the light emitted from the whole body, or any of its parts, 

 is composed of a vast number of instantaneous scintillations, 

 closely approximating to one another at the centre of the ''phos- 

 phorescent'' portions, but clearly distinguishable at the edges 



(Fig- 5)- 



Occasionally there may be seen isolated sparks at the extreme 



limit of the luminous areas, or even beyond. 



Quatrefages extended his observations to higher forms, 



where the phosphorescence is intimately associated with con- 



