STRUCTURE OF NOCTILUCA. 49 



inspection, will be found to swarm with little points 

 of most translucent jelly, requiring close examination 

 even to detect their presence, and yet so numerous 

 that 30,000 of them have been calculated to be con- 

 tained in a cubic foot of highly luminous sea- water. 

 The appearance of these living gems the reader will 

 find delineated in PI. I. fig. 3, and during the summer 

 season will have little difficulty in verifying the most 

 prominent circumstances connected with their history. 

 The name Noctiluca* conferred upon these minute 

 organisms is indicative of the remarkable faculty that 

 they possess of emitting a brilliant light. When a 

 vase filled with sea-water, crowded with these little 

 creatures, is placed in a dark chamber, the slightest 

 agitation is sufficient to excite their phosphorescence, 

 and the smallest undulations upon the surface are in- 

 dicated by luminous circles. On examining one of 

 them very attentively with a powerful microscope, 

 it is further observable that the light given out is not 

 universally diffused throughout the substance of its 

 body, but is confined to minute shining points scat- 

 tered here and there, which make their appearance in 

 rapid succession, and as suddenly vanish : so that 

 evidently there is no special organ to which the lumi- 

 nous appearance can be referred, as in the case of the 

 glowworm and other phosphorescent creatures. In 

 size, these stars of ocean are almost microscopic, the 

 largest of them not much exceeding the dimensions 

 of a pin's head ; but the amazing numbers in which 

 they crowd the seas amply make up for their minute- 

 ness ; at certain seasons indeed it may be literally 



* Node, by night j luceo, I shine. 



D 



