PHOSPHORESCENT ORGANS 



357 



Deep-sea Teleostean fish are variously modified in adaptation to 

 their peculiar environment, and among the most characteristic 

 structures developed in them are the phosphorescent organs. 

 These differ considerably in the various genera and in the 

 different parts of the same animal. The more elaborate phos- 



Fio. 343. 



A, early stage in the development of the scales of the Minnow, Leitciscus phoxlnus, L. B, 

 portion of the free edge of the dorsal fin of a young Siluroid, showing the actinotrichia 

 underlying the lepidotrichia at the growing margin. C, transverse section of the developing 

 lepidotrichia of the Trout, Salmo truta, L. All enlarged. , actinotrich ; b.m, basement 

 membrane; c.t, connective tissue; e, growing edge; I, lepidotrich ; s, pocket lined with 

 scleroblasts enveloping the developing scale, sc ; w, web of fin. 



phorescent organs have a cellular lens set in the opening of a cup, 

 which contains an epithelium of large cells. These are the cells 

 which secrete the light-giving substance, and the walls of the cup, 

 generally covered with pigment, act as a reflector (Fig. 345). 

 Organs of this character may be present on the head or body, and 

 may be distributed in regular lines, or scattered over the whole 



