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FISHES 



i. The PJiotoplwres of Scopelidce. — In these small pearl- 

 like organs the essential or special body which appears to pro- 

 duce the light is a somewhat flattened circular disc composed 

 of thin plates lying one over the other, nearly parallel to the 



Fig. 30. — Microscopic Structure of Luminous Organs of Fishes. A, Section 

 of pearl-like organ of Myctophum, after von Lendenfeld. B, Section of head of 

 Ipnops, after Moseley. C, Portion of same more highly magnified. D, Longi- 

 tudinal section of lateral line of Halosanropsis, after von Lendenfeld. gl., gland ; 

 sc, scale; ph., phosphorescent organ; s.o., sense-organ. 



surface of the skin ; between the plates are nuclei. This special 

 body lies between two overlapping scales, the outer of which is 

 transparent and thickened to form a lens by which the light is 

 concentrated. The inner scale is thin and concave and on its 

 inner surface is covered with reflecting substance, internal to 

 which again is a layer of pigment. The inner scale thus evi- 



