560 



THE BIOLOGY OF MARINE ANIMALS 



it has been possible to carry out the luminescent reaction in vitro with 

 extracts from a few species, and to gather a great deal of information by 

 this means about the processes involved. The animal which has been most 

 useful in this regard is Cypridina which is strongly luminescent, and yields 

 potent light-producing extracts that can be kept in an active condition for 

 long periods. 



It was early discovered by Spallanzani that when the luminous material 

 of medusae was dried and subsequently moistened it would still give off 

 light. Similar observations have since been made on other forms including 

 pennatulids, ostracods, copepods, Phyllirrhoe, Pholas and Pyrosoma. 



Fig. 13.23. Luminous East Indian Fish Harbouring Symbiotic Bacteria 



{Above) Anomalops katoptron. (Below) Photoblepharon palpebratus. In both animals 

 the light-gland lies below the eye. (After Buchner (11), and Harvey, 1940.) 



Two requirements for the luminescent reaction to proceed are water 

 and oxygen. The reaction is an oxidation, although the amount of oxygen 

 necessary is sometimes very small. No light is produced by photogenic 

 extracts of Pholas, ostracods and pennatulids in the absence of oxygen, nor 

 by Noctiluca. A mixture of Cypridina luciferin and luciferase still gives off 

 light at an oxygen pressure of less than 0-0007 mm Hg, but an exact thres- 

 hold figure is not available. With purified extracts the relationship between 

 light intensity and oxygen concentration takes the form of a rectangular 

 hyperbola, 50% of maximal intensity being attained in 1-9 %0 2 . There are 

 a few forms, however, in which luminescence can occur in the absence of 

 free oxygen, namely certain radiolarians, the medusae Pelagia and Aequorea, 

 and certain ctenophores. It would appear that this is due to an alternative 

 source of oxygen in the preparations that were used (30). 



Dubois demonstrated in 1 887 that the photogenic reaction in the piddock 

 Pholas dactylus involves the interaction of two substances, which he called 

 luciferin and luciferase. Luciferin is relatively heat-stable, whereas luci- 

 ferase is heat-labile and is destroyed on boiling. A separate preparation of 



