ASSOCIATIONS 



621 



Symbiotic Bacteria and Luminescence 



Certain luminescent organisms owe their light to symbiotic bacteria, 

 and the physiological and morphological implications of this relationship 

 have been outlined in Chapter 13. Following the discovery of symbiotic 

 bacteria and mycetozoa in various higher plants and animals, frequent 

 claims have been made that the luminescence of many groups of animals 

 is due to symbiotic bacteria, but few of these conjectures have been sub- 

 stantiated. Luminescent animals which owe their light to bacteria are 



Fig. 14.24. Specimen of Euprymna morsei with Mantle Cavity 

 Opened to Expose Ink Sac and Light-organs 

 a, Accessory nidamental gland; i, ink sac; /, light-organ (x 1). (After Kishitani, 1928.) 



various myopsid squid and teleosts, and bacteria have also been implicated 

 in the luminescence of tunicates. 



The luminescent bacteria of myopsid squid have been studied in some 

 detail, especially by Pierantoni, Kishitani and Herfurth. The subject is 

 reviewed by Harvey (42), who also gives a detailed account of factors 

 affecting the luminescence of free-living bacteria. In myopsid squid the 

 luminous glands or accessory glands lie close to the anus and ink sac, 

 and are intimately associated with the accessory nidamental glands 

 (Figs. 13.21 and 14.24). The simplest condition is seen in Loligo, where the 

 accessory glands are open to the exterior and consist of a mass of epithelial 

 tubes which enclose luminous bacteria. In many cuttlefish the accessory 

 glands are distinct and more complex, and contain several kinds of epith- 

 elial tubes and bacteria, only one variety of which is luminescent. 



The luminescence of the accessory glands has been observed in Sepiola 



