82 



THE NATURE OF ANIMAL LIGHT 



make up tlie marine plankton, Noctiluca, dinoflagellates, 

 jelly-fish, ctenopliores and even the sessile sea pens. 



We know that luminous bacteria occasionally lose the 



c.fasifr 



Fig. 30. — Sectional view of photogenic organ 

 of a squid, Calliteuthis (ajter Chun), phot., photo- 

 genic cells; I, U, lens; n, nerve; spec, "Spiegel"; 

 pg., pigmented screen; c. fusif., spindle-shaped 

 reflector cells; chr., chromatophore color screen. 



power of lighting and that on certain culture media they 

 develop as non-luminous forms. Luminescence is not 

 indispensable to them. The same is true of some of the 



