LIGHT PRODUCTION IN CEPHALOPODS. 185 



TABLE V. 



COMPONENT PARTS OF THE CEPHALOPOD PHOTOPHORE. 



I. Primary (photogenic tissue). 



1. Photogenic cells. 



2. Veins and arteries. 



3. Nerves. 



4. Connective tissue. 



II. Secondary (accessory structures). 



1. Pigment cup (almost always present, but sometimes lacking where photo- 



phore is surrounded by other pigmented tissue, as the ink sac or 

 eyeball). 



(a) Chromatophores. 



(b) Specially modified pigment cells (an adaptation of preceding ?). 



2. Reflector, or Tapetum. 



(a) Nucleated cells. 



(b) Fibers. 



3. Scale cells, or "Schuppenzellen" of Chun. 



(a) as reflector. 



(b) as lens or cornea. 



(c) in photogenic tissue. 



4. Lens. 



(a) Fibrillar. 



(b) Cellular. 



(1) Connective tissue. 



(2) Modified mantle musculature. 



5. Diaphragm. 



(a) Chromatophores. 



(b) Muscles. 



6. Windo'vv. 



7. Mirror. 



8. Accessory photophores ("double organs"). 



The duplex photophores deserve a further word. These 

 comprise two separate masses of photogenic tissue so closely 

 associated together that the conclusion seems unavoidable that 

 in some way they function in common. Organs of this type 

 seem to have been first discovered by Chun, who described them 

 in some detail for a number of species. There is small doubt 

 that histological examination will show the occurrence of similar 

 organs in many other instances also. The double crescentic 

 subocular photophores of certain Cranchiidse have been briefly 

 described on an earlier page. Lycoteuthis (and most probably 

 Nematolampas also) 17 possesses a number of duplex organs, the 



17 Nematolampas certainly agrees in having the terminal subocular photophores 

 equipped with an accessory photophore. The other organs mentioned have not 

 yet been investigated. 



