82 THE NATURE OF ANIMAL LIGHT 



make up the marine plankton, Noctiluca, dinoflagellates, 

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

 "We know that luminous bacteria occasionally lose the 



plat 



c/iui/V 



FiG. 30. — Sectional view of photogenic organ 

 of a squid, CalHteuthis (after Chun), phot.^ photo- 

 genic celle; I, l'-, lens; n, nerve; spec., "Spiegel"; 

 p(j., 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 



