88 SYMBIONTICISM AND THE ORIGIN OF SPECIES 



teroid" stages of light-producing bacteria that have adapted 

 themselves to an intracellular life. It is not clear from 

 Buchner's discussion why he considers these forms fungi. 

 So far as their morphology is concerned they might as well 

 be bacteria. Although it is immaterial whether they are 

 called fungi or bacteria, they are nevertheless intracellular 

 microsjrmbionts. 



The most remarkable instances of luminiferous organs 

 associated with known microsymbionts occur in certain 

 cephalopods. Pierantoni ('17, '18) and Chun ('10) have 

 described the development of the organs in Rondeletia 

 minor, Sepiola intermedia and Pterygioteuthis maculata 

 (fig. 2). The luminiferous organ in the adult has the 

 general appearance of an eye. It possesses a "tapetum" 

 (dark screen) in the deep peripheral part of the organ. 

 Next to the tapetum nearer the surface is a contractile 

 reflector. In the central part of the organ and superficial 

 to the reflector is a gland-like structure containing the 

 luminiferous bacteria. A lens is present in front of the 

 luminiferous body, and is covered by transparent epithe- 

 lium. The development of this organ is remarkable in 

 that it utilizes accessory structures in its formation. There 

 are accessory ''nidamental glands" found in these animals 

 which later become the luminous element in the light 

 organ. Bacteria are associated with these glands, but 

 they are usually not luminiferous in the earher stages of 

 development. Modifications of these glands take place, 

 and they come into association with the ink bag, which 

 ultimately forms the tapetum. Between the ink bag and 



Fig 2. Diagrammatic Sections through the Light Organs of 



Rondeletia minor (A), Sepiola intermedia (B) and 

 Pterygiotheuthis maculata (C) 

 Ep = epidermis, Le = Lens, Lu = luminous part, P = pigment (in A 

 and B, ink bag) Re = reflector. A and B from Pierantoni, C from Chun 

 (after Buchner). 



