STRUCTURE OF LUMINOUS ORGANS 



79 



which enters the nerve, for the light of these organs is 

 under the control of the animal and may be flashed 

 ^^atwill.'* 



All gradations in complexity of light organs may be 

 found from the condition in the shrimp just described to 

 that found among the squid and fish. Figs. 29 and 80 are 



Fio. 27. — Sectional view of photogenic organ of Sergestes prehensilis (after Terao). 

 bm, basement membrane; cs, connective strands of photogenic layer; hy, hypodermis; 

 h, h, h, layers of lens; le, lens epithelium; n, nerve; ph, photogenic cells; pi, pigment layer; 

 r, reflector; th, theca. 



sections of two of the more complicated types found in 

 squid. The explanation given to the various structures is 

 that of Chun (1903) to whom we are indebted for a careful 

 histological investigation of these forms. It will be noted 

 that in addition to photogenic and lens tissues there are 

 various types of reflector cells and a line of pigment about 

 the whole inner surface of the organ to effectively screen 

 the animaPs tissues from the light. In one form (Fig. 



