HISTOLOGY OK THE LIGHT ORGANS. 



II 



is a layer of highly insoluble material, which, as already mentioned, is called 

 the "reflecting layer." The light is generated in the glandular material, 

 the "driisenkorper," d. K., and passes through the funnel-shaped opening, 

 finally emerging through the lens, I, into the air. 



I 



T. Section of Pholuris pennsylvanica. 



II. Section of I'hotinus pyralis. P = piguient. 



Ill 



III. Transverse section of Pholinus pyralis (dia- 

 grammatic). 



The right-hand half shows the arrangement and 

 distribution of the tracheae, while the left-hand 

 half shows the modification of the luminous 

 tissue at the point of attachment of the breath- 

 ing muscles. 



G, testes; /, intestine; L, true photogenic tissue; 

 R, reflecting layer; 5. spiracle or stigmatum; 

 Sp, spiral organs (function uncertain); T, 

 main tracheae to photogenic organ; Tb, main 

 respiratory trachea;; M, muscle fibers. 



Fig. 4. 



This description seems a little fantastic, for optically the system is 

 extremely inefficient. The low reflecting power which must obtain in the 

 so-called "reflecting layer" and the roundabout way for the light to reach 



d.K.-i 



i.R.- 



A, Section through the ventral region of a lish, Maiirulicus 

 pennanti. 



B, Section through a light organ of a fish. (After Mangold.) 



Fig. 5. 



the lens (granting that the lens and the reflector have sufficient figure to give 

 directive power) does not carry conviction to the idea that this is a miniature 



