BASIS OF ANIMAL PHOSPHORESCENCE. 113 



dentally produced at first as a result of some necessary chemical 

 changes in the body may be utilized in the course of the race 

 history of an organism (as among birds which use heat evolved 

 by the metabolism of their tissue for the process of incubation), 

 it is equally conceivable that light incidentally produced as the 

 result of a necessary combustive process of life may eventually 

 be utilized in the race history of some species, and thus that 

 which is an end in one organism may become the means to a 

 remoter end in another organism. The mere fact that in some 

 animals the light is of no apparent use to them is no reason to 

 doubt that it may be of some use to others, in which the pro- 

 duction of light becomes the end and purpose of some definite 

 structure, and is even brought in connection with the mechanism 

 of the will. 



While the production of light may be regarded as belonging 

 to the same ultimate cause as that of heat, the proximate cause 

 of the luminosity in the animal kingdom may be due to a variety 

 of secondary circumstances. 



Thus (i) an organism may appear brilliant in the dark, owing 

 to the presence of luminous bacteria in the tissue. 1 In such a 

 case, the luminosity of the organism may be considered as a 

 pathological phenomenon. 



In another instance (2) the organism may appear luminous 

 also on account of the luminous bacteria which live in a sym- 

 biotic fashion in the tissue of the organism, but this cannot be 

 called a disease, as the animal suffers no bad consequence, and 

 may even be benefited by it. 2 



In still another case (3) transparent pelagic organisms like 

 some Crustacea may appear phosphorescent from containing in 

 their stomachs phosphorescent food, which shines through the 

 body of the organism. In a case like this their excrement is 

 also phosphorescent. 3 



1 See Giard : Sur 1'infection phosphoresc. des Talitres et autres crustacees. 

 Compt. Rend., Sept. 23, 1889, P- 53- Peter Schmidt : On the Luminosity of 

 Midges (Chironomus). Zool. Jahrb. Abth. f. Syst. Geog. und Biologie, Bd. VIII, 

 Heft I, 1894. Ann. and Mag of Nat. Hist., Vol. XV, 1895 (translated by Austen). 



2 R. Dubois : Sur le role de la symbiose chez certains animaux marins lumineux 

 [Pelagia et Pholas]. Compt. Rend., Tome CVII, 1888, p. 502. 



3 H. N. Moseley: Notes of a Naturalist, p. 498. 



