554 



THE BIOLOGY OF MARINE ANIMALS 



from the cyathozooid, the test cells pass into the circulation and give rise 

 to the light-organs of the primary ascidiozooids. 



Analogous conditions obtain in the Salpidae. In the solitary form of 

 Cyclosalpa pinnata, for example, there are five pairs of luminous glands 

 lying laterally between the body muscles, whereas in the aggregated form 

 there is a single organ on each side of the body. 



Only a few examples can be considered of the many diverse kinds of 

 photophores occurring in fishes. Among selachians the small shark Spinax 



Luminescent 

 cells 



% 

 (a) '^2L_ (b) 



Fig. 13.15 (a). Ascidiozooid of Pyrosoma 



The luminous test cells are located at the entrance to the branchial chamber. (After 

 Buchner (11).) 



Fig. 13.15 (b) Luminous Test Cells of Pyrosoma Containing Intracellular 

 Inclusions, sometimes Regarded as Bacteria. (After Buchner (11).) 



niger may be mentioned (Fig. 13.16). This animal, found at depths of 

 300-3,000 metres, gives off a bright glow from certain regions of the body. 

 The luminous organs responsible lie in thickenings of the epidermis (Fig. 

 13.17). Each organ contains a group of from six to eight photogenic cells, 

 the distal ends of which converge into a central mass containing secretory 

 luminous material. Distally there are a few large cells which represent a 

 lens, and lying about the organ there is a layer of chromatophores which 

 also show a tendency to extend in front of the luminescent cells like an 

 iris diaphragm (34, 35). 



In many deep-sea teleosts, represented by forms such as the lantern 

 fish Myctophum, the hatchet fish Argyrope/ecus, Stomias, Photostomias 



