TISSUES OF LIGHT-PRODUCTION 



139 



The final development is seen in Figure 129. The invaginated cell 

 mass is differentiated into a proxi- 

 mal layer which produces luciferase, 

 and a distal portion which has grown 

 transparent and refractive to be used 

 as the lens. The proximal connec- 

 tive-tissue layer has acquired a dense 

 white appearance that enables it to 

 be used as a reflector, and behind it 

 lie the pigment cells in their usual 

 position in a light-organ. 



The organ pictured in section, as 

 Figure 129, is not yet fully formed. 

 Greene presents a figure of an adult 

 photosphere, but this stage in Figure 



129 is Sufficient for the purpose of FIG. 128. Still more advanced stage than 



understanding the fully formed organ, ^ '*7 of P<fc%, light-organ. LU- 



... minous cells (lu.c.) of organ beginning to 



which differs from it Only in Size and differentiate from lens cells (I.e.), also traces 



some trifling points of form. of r ir eflector -\ the le " ei l n the ^ me 



as Figure 1 26. (After C. W. GREENE.) 



Light-organs have been described 



in the young of some birds, especially on the edge of the mouth in the 



nestlings of an Aus- 

 tralian finch. These 

 were rightly supposed 

 to be of use in guiding 

 the parent when deliv- 

 ering food to its young 

 when the time or place 

 rendered the nest 

 dark. 



Chun found that a 

 weak light appeared 

 to be given off from 

 the papillae in an or- 

 dinary darkness until 

 the room was made 

 absolutely dark, when 

 no glow whatever was 

 apparent. Also his- 

 tological investigation 

 showed the entire ab- 

 sence of any cells which appeared to secrete a luciferase. It was 

 therefore concluded that the organ was a structure that could collect 



lu. c. re/. 



FIG. 129. Young but fully formed light-organ of Porichthys. 

 lu.c., luminous cells; ref., reflector; I.e., lens cells. Other let- 

 tering the same as Figure 126. (After C. W. GREENE.) 



