No. 3.] PHOSPHORESCENT ORGANS. 677 



marked in the nasal, dorsal, anal, and mandibular lines. In 

 these lines they often reach a length of 2 mm., and are three 

 and four parted at their ends. 



III. Structure of the Phosphorescent Organs. 



Organs from different parts of the body have a common 

 general structure, differing only in minor details. It will, 

 therefore, be sufficient to describe a typical organ in detail and 

 later compare with it those organs which have a specialized 

 form or structure. 



The epidermis of Porichthys has no scales and is richly 

 supplied with large, club-shaped mucous cells in all stages of 

 development. The dermis is quite a thick layer of dense con- 

 nective tissue bearing blood vessels, nerves, and pigment cells. 

 The phosphorescent organs are imbedded in the deeper portion 

 of this dermis. 



Each organ consists of four parts (PI. XXXVIII, Fig. 4, and 

 PI. XXXIXf Figs. 5 and 9), the lens, the gland, the reflector, 

 and pigment. 



I . Tlie Lens. 



In a typical organ, from the anal or ventral row, for example, 

 the outer or more superficial portion of the organ consists of a 

 group of cells, the lens (PI. XXXIXf Fig. 5, /). The surface 

 of the lens directed toward the exterior, the distal portion, is 

 oval or spherical in outline, while the deeper or proximal portion 

 is projected into a more or less pronounced subconical form. 

 The cells of the lens are polygonal in form in the center of the 

 structure, becoming flattened toward the surface. At the distal 

 surface the cells are quite regular and form a pavement-like 

 layer (PI. XXXIX" Figs. 5 and 9), but in the deeper conical 

 portion the cells are very irregular in form, often with processes 

 which interlace in a confused mass at the extreme proximal part. 

 The lens cells have a small oval nucleus which is very sharply 

 defined in contrast with the modified cytoplasm. The cell body 

 is very dense, homogeneous, and highly refractive. The co- 

 agulation of this dense substance by reagents often slightly 



