Insects. 55 



Noie on the Luminous Appearance of the Sea, with descriptions of 

 some of the Entomostracous Insects hy which it is occasioned. 

 By W. Batrd, Esq. M.D., Assist. Zool. Dep. British Museum. 



The luminous appearance of the sea, so often mentioned by voya- 

 gers, is, especially within the tropics, very beautiful and interesting, 

 and depends in a great measure upon the presence of minute Crus- 

 tacea — such as the Entomostraca more particularly — and Medusae, 

 the different kinds of animal producing a different kind of luminous- 

 ness. This I may illustrate by an extract or two from a journal kept 

 during a voyage to India. 



" May 28, 1832, lat. 1° 50' N. long. 24° 07' W, In the evening the 

 sea, especially in the wake of the ship, where the water was agitated 

 by the ship's way through it, was splendidly luminous; it presented a 

 truly brilliant appearance at times, for the beautiful brilliancy of the 

 luminousness was not equal at one time to what it was at another. — 

 Sometimes the broad bright flash, which had distinctly occasionally a 

 bluish colour, was vivid enough to illuminate the sea for some distance 

 round, while the most splendid globes of fire were seen wheeling and 

 careering in the midst of it, and by their brilliancy outshining the ge- 

 neral light. These bodies were generally too deep in the water to be 

 caught by throwing a bucket or net overboard. 



" May 29. Lat. 0° 35' S. long. 26° 02' W. The sea was very lu- 

 minous again this evening, but differed from last night in there being 

 fewer large globes deep in the water, and a much greater abundance 

 of bright small specks on the surface. Drawing a bucket-full of water 

 up, about 8, P.M., I allowed it to remain quiet for some time, when 

 upon looking into it in a dark place, the animals could be distinctly 

 seen emitting a bright speck of light. Sometimes this was like a sud- 

 den flash, at others appearing like an oblong or round luminous point, 

 which continued bright for a short time, like a lamp lit beneath the 

 water, and moving through it, still possessing its definite shape, and 

 then suddenly disappearing. When the bucket was sharply struck 

 on the outside, there would appear at once a great number of these 

 luminous bodies, which retained their brilliant appearance for a few 

 seconds and then all was dark again. They evidently appeared to 

 have it under their own will, giving out their light frequently at vari- 

 ous depths in the water, without any agitation being given to the 

 bucket. At times might be seen minute but pretty bright specks of 

 light dart across a piece of water, and then vanish, the motion of the 

 light being exactly that of the Cyclops through the water. Upon re- 



