E. NEWTON HARVEY . 15 



is due to a characteristic of the chemiluminescent reaction or to ab- 

 sorption by pigments. The extreme range of color appears in the 

 railroad worm Phrixothrix with both yellow lights and also a bright 

 red light in the head, which is not connected with any red pigment 

 detectable with the eye. 



The ophiuroids, despite considerable histological study, present 

 many unsolved problems of physiological and biochemical nature, 

 and the same may be said for the balanoglossids and the tunicates. 

 Luminous species are abundant among surface marine organisms and 

 are easily obtainable. 



The considerable number of fish whose light is not due to luminous 

 bacteria are in the same category as the squid. They are mostly deep 

 sea forms with photophores, not favorable for chemical work but 

 presenting many physiological problems in connection with nerve and 

 hormone excitation. They deserve intensive investigation, whenever 

 the occasion allows. In fact it seems certain that luminous organisms 

 as a whole can supply much information important for an under- 

 standing of fundamental processes in even.' field of biology. 



