106 Animal Luminescence 



the linkages of organisms, is illustrated by the evi- 

 dence that in some cases, such as luminous cuttle- 

 fishes, the light is produced by nests of Bacteria. 

 They are like those that we see in the dark on the 

 glistening surface of the haddock hung up to dry; 

 but they are living in regularized partnership with 

 the animal. In some cases, therefore, the luminescent 

 animal shines with a borrowed light. 



Many beetles eat wood, but that is Spartan diet. 

 It is not surprising, therefore, that some of the 

 beetles which habituallv bore in fresh wood have 

 learned to grow a mould that yields what is called 

 "ambrosia." This fungus lives on the wood and its 

 sap, and spreads over the walls of the tunnels that 

 the beetles make. The fungus collects, concentrates, 

 and prepares the food, making ambrosial bodies for 

 the beetles and their grubs. In some cases the beetles 

 never swallow the dust of the wood through which 

 they bore; they feed on ambrosia. The fungus does 

 not seem to form spores or propagative elements, so 

 it is probable that the beetles infect a new tree with 

 surplus vegetative ambrosia cells which have passed 

 out undigested from the food-canal. 



Sometimes there is a triple alliance. Thus certain 

 gall-midges that attack flowers of mulleins, scrophu- 

 larias, and capers, provoke strange galls, inside which 

 an ambrosia fungus flourishes. Gall-midge, mullein, 

 fungus — a triple alliance. The hollow petioles of the 

 Tachigalia tree in British Guiana are the homes of 

 certain little beetles that have established an ali- 

 mentary partnership with minute mealy bugs. These 



