332 ALLMAN ON NOCTILUCA. 



irritation from other animals which may have been confined in 

 the same jar, have been known to light np for an instant the 

 entire jar with its beautiful phosphorescence. The towing-net 

 which has been employed in its capture Avill continue, when 

 shaken in a darkroom, to exhibit the most brilliant scintilla- 

 tions as long as the Nociilucce which may adhere to it are 

 still alive, and I have seen this phenomenon presented for 

 died, and the Avater has even begun to exhale a putrid odour, 

 Noctiluca may be seen with as much vigour as ever, ready 

 more than thirty hours after the net had been withdrawn 

 from the sea, and when only a slight dampness continued to 

 be retained by it. 



Noctiluca differs from Beroe, another of the most brilliantly 

 luminous animals of our shores, in the fact that a prolonged 

 withdrawal from sunlight is not necessary in order to render 

 it capable of manifesting phosphorescence ; Avhile Beroe, as I 

 have elsewhere shown/ must be kept in the dark for some 

 time before its pliosphorescence can be elicited by any irrita- 

 tion. Noctiluca, on the other hand, will show no impair- 

 ment of its phosphorescent powers even at the moment of 

 its being removed from broad sunlight into a darkened 

 room. 



I have satisfied myself that the special seat of phosphor- 

 escence in Noctiluca is the peripheral layer of protoplasm 

 Avhich lines the external structureless membrane. By a 

 little careful management Noctiluca may be examined by 

 night when in the act of emitting its light under the micro- 

 scope. I have found the addition of a drop of alcohol to 

 the water containing specimens of the animal on the stage 

 to afford a very convenient stimulus for this purpose. The 

 entire surface of the body Avill then instantly become lumi- 

 nous with a light strong enough for transmission through 

 the microscope Avith a half-inch object glass. Unlike the 

 momentary phosphorescence elicited by simple agitation, 

 that produced by the irritation of the alcohol Avill generally 

 last several seconds Avith full intensity, and Avill then gradu- 

 ally disappear. Before the final extinction of the light the 

 animal Avill present the appearance of a luminous ring pro- 

 jected on the dark stage. This phenomenon is at once 

 explained by the supposition that the phosphorescence is 

 confined to the peripheral portions of a transparent sphere, 

 for by this time the light has become so Aveak as to be in- 

 appreciable, except Avhere tOAvards the edges of the projected 

 sphere a greater depth of the luminous stratum lies in the 

 direction of vision. 



' Troc. Roy. Soc. Ediii.,' iS62. 



