Causes of Phosphorescence. 275 



A light which, to the naked eye, appears uniform and tran- 

 quil, shews itself scintillating under the microscope. 



5. The viscous humour which envelopes and penetrates the 

 ovaries, seems to be especially susceptible of acquiring this 

 communicated light, which is constantly reinforced by fric- 

 tion, and reappears even when it seems to have ceased. 



May not the light emitted by living fishes, by Actinias, and 

 by many other animals covered with mucosity, be sometimes 

 merely communicated. 



6. The relations which exist between the production of 

 light and the sexual functions are evident in the Coleoptera, 

 although the connection of the small luminous sacs with the 

 reproductive organs may remain concealed. With many 

 marine hermaphrodite animals, phosphorescence appears to 

 be a means of defence and protection analogous to those of 

 another kind which exist in the Brachinus crepitans, the 

 cuttle fish, the frog, or to the discharges of the torpedo. What- 

 ever it may be, the air and the sea have their phosphores- 

 cence. 



7. As yet it is only among the Annelids, and of them only 

 in the Photocharis, that a peculiar phosphorescent organ has 

 been discovered ; it is external, tufted, frequently giving out 

 light, similar to a thick cirrus, shewing a largely cellular 

 structure, and formed within of a mucilaginous substance. 

 The expanded base of the marginal cirri in the Thaumantias 

 (Acalephs) may be regarded as phosphorescent organs of an 

 unusual kind. The ovaries are more probably luminous, pas- 

 sively, and in a secondary manner, although their minuteness 

 and transparency have prevented our ascertaining whether 

 the organs of phosphorescence are placed near them, as for 

 instance in the Polynoe and Pyrosomas. 



8. The production of light is evidently a vital act, very 

 similar to the development of electricity ; an act which, being 

 completely individual, becomes more feeble, and ceases on 

 too frequent repetition, which reappears after a short in- 

 terval of repose, to the production of which, absolute in- 

 tegrity of the organism is not necessary, but which some- 

 times manifests direct connections only with the nervous 

 system. 



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