220 FOUNDERS OF OCEANOGRAPHY 



togen" and " photophelein " — which, we may hope, further 

 research will show to be unnecessary. Harvey showed that 

 these essential substances might be dried, extracted with 

 ether, or treated in various other ways, without affecting 

 their power of subsequently producing Hght. The process, 

 then, is quite independent of the animal body in which the 

 substances were produced, and so far is a physico-chemical 

 phenomenon. Similarly, Giesbrecht found that he could 

 thoroughly dry some of the luminous Copepoda at Naples, 

 and months afterwards caused these dried bodies to produce 

 hght by adding a httle sea-water. 



The power of luminescence has only been definitely estab- 

 lished in the case of about half a dozen kinds of Copepoda 

 (Plate XIV, Fig 3), but some of these are widely distributed, 

 and have been frequently observed. The light-glands are 

 scattered over various parts of the body and pour their 

 secretion out to the exterior. On a voyage to Australia 

 by the South Atlantic, I observed on many occasions these 

 luminescent Copepoda caught in fine nets on the sea-water 

 bath taps ; and, having isolated one of the sparkhng speci- 

 mens under the microscope in the dark, have watched how 

 its luminous secretion was emitted on stimulation, and, 

 spreading from the head along the dorsal surface, floated 

 away from the body and hung in the water for some seconds 

 as a luminous cloud. This has been interpreted as pos- 

 sibly of use as a " sacrifice -lure." The Copepod, when in 

 danger, emits the glowing secretion and escapes, leaving the 

 luminous cloud in the water to distract the attention of the 

 enemy. 



In the luminescent Schizopoda (such as Euphausia and 

 MeganyctipTianes) the Hght-producing organs are conspicuous, 

 highly organized structures, comparable in some respects 

 with an eye or a bull's-eye lantern, and having a source of 

 Hght with a reflector behind and a lens in front. They 

 were, in fact, supposed to be eyes at first, and are described 

 in the older books under the term " accessory eyes." It 



