NOCTILUCA MILIARIS. 15 



remain as a thick stratum, whilst the shghtest agitation of the jar 



in the dark will cause instant emission of their light. This is of 



a beautiful greenish tint, and is so vivid that absolute darkness is 



by no means necessary to render it visible, for even by ordinary 



lamp-light it is quite perceptible. The emission of the light is but 



of instantaneous duration, and rest is needed for a repetition of the 



display. A few moments, however, will suffice for this, and the 



light is then as brilliant as before. Any other animals confined in 



the glass coming in contact with the Noctiluca cause it to light up 



the jar with its beautiful phosphorescence. Even the towing net, 



which has been employed in their capture, will continue, when 



shaken in a dark room, to exhibit brilliant scintillations provided 



any of these organisms are adhering to it, Noctiluca differs from 



Beroe, another of the most brilliantly luminous animals of our 



shores, in the fact that a prolonged withdrawal from the sunlight 



is not necessary in order to render it capable of phosphorescence, 



whilst Beroe must be kept in the dark for some time before its 



luminosity can be excited by irritation. Noctiluca, on the other 



hand, will show no impairment of its powers, even at the moment 



of its being removed from broad sunlight into a darkened room. 



The special seat of phosphorescence is most probably in the 



peripheral layer of protoplasm, which lines the external 



membrane. An easy way of examining this protozoon is obtained 



by placing it in an excavated glass slip with some sea water, a few 



inches off place a strip of white blotting paper, at the end of this 



make a tiny pool of alcohol, this will gradually drain off into 



the miniature sea in which the Noctiluca is disporting itself. 



As soon as the alcohol becomes mixed with the sea water, the 



light flashes out from the whole surface of the body, and as the 



proportion of the irritating spirit increases in the cell, so will the 



brilliancy of the luminosity. After a few seconds this gradually 



diminishes till nothing is left but a luminous ring, which soon goes 



out, and the brief life of the Noctiluca is concluded. 



EXPLANATION OF PLATE I. 



Fig. 1. — Noctiluca miliaris : a, the outer surface of the "tooth" ; h, 

 oral aperture ; c, the position of the supposed anal aperture. 



