Fishes Photoblepharon and Anomalops. 51 



whose combustion is intraglandular but extracellular, but an organ for 

 the nourishment of symbiotic luminous bacteria. On this view the 

 extraordinary richness of the blood-supply is at once apparent — to 

 supply the oxygen for respiration of the organ cell, for respiration 

 of the bacteria, and for the production of light by the bacteria. 

 Luminous bacteria require an unusually abundant supply of oxygen, 

 as those who are familiar with the growth of them will readily under- 

 stand. 



On this view the existence of pores in an organ which does not 

 produce an external secretion becomes explicable — namely, a means 

 of exit of dead bacteria. It is very likely that other fish may also 

 be found to possess luminous organs for the growth of luminous 

 bacteria. To decide this it will be necessary to study the living 

 animals, as no certain remains of bacteria are to be made out in fixed 

 material. A fish which I suspect may prove to be similar to Photo- 

 blepharon and Anomalops is Monocentris japonica of Japan. My 

 suspicion is based on the fact that the light of this fish, two specimens 

 of which I observed at Misaki in 1917, is produced continuously day 

 and night and without change in intensity, just as the Banda fishes. 



The view that animal light is due to bacteria is not a new one. It 

 has been advocated by Pierantoni (1918) for some years. He had 

 grown cultures of luminous bacteria from the luminous material of 

 squid and has even gone so far as to suggest that in forms where 

 no bacteria can be demonstrated we are dealing with ultramicro- 

 scopic organisms similar to ultramicroscopic pathogenic forms sup- 

 posed to be present in filterable viruses. While it is certainly not 

 true that the light of all forms is due to luminous bacteria, I think 

 the chemical evidence which follows, together with the ocular evi- 

 dence already described, is very strongly in favor of the view that the 

 fight of these fishes is due to symbiotic luminous bacteria. 



LACK OF OXYGEN. 



One of the conspicuous anatomical peculiarities of the light-organ 

 is its rich supply of blood-vessels. These can be seen in life, running 

 from the lower (principally) and upper edges of the organ to branch 

 over its surface into capillaries which run between and parallel to 

 the columns of luminous material. The organ is also in a position 

 just anterior to the gills to receive fully oxygenated blood, and in 

 cutting the organ out blood flows freely, showing the presence of 

 large arteries in this region. It is not surprising, then, to find that 

 the organ is very sensitive to lack of oxygen, the light disappearing 

 promptly in its absence. This can be shown for both Anomalops and 

 Photoblepharon by three methods. 



First, it may be readily observed that the light-organs of fish 

 dying in sea-water from lack of oxygen become dimmed. If the fish 



