PHOSPHORESCENT ORGANS 



179 



murrayi 1 (Fig. 371, C) has a singular organ, probably luminous, 

 beneath the transparent superficial bones of each side of the roof of 

 the skull Another member of the same family (Scopelus benoitii) 

 is interesting in having a phosphorescent organ in the middle of 

 the back, which is directed backwards. An American genus of 

 Batrachidae (Porichthys) has about 350 photophores in relation 

 with the lateral sense-organs of each side of the head and body. 2 



FIG. 96. Pachystomias microdon, showing the two rows of phosphorescent organs 

 along the side of the body, and the anterior and posterior suborbital luminous organs. 

 ( After Giinther.) 



The existence of luminous organs has also been noticed in the 

 Haddock (Gadidae)? A primitive form of photophore, distributed 

 in considerable numbers on the head and trunk, either in lines or 

 diffused over the surface, exists in eleven species of Selachii 

 (Spinacidae), of which some are known to be luminous. 4 



Diversity of structure is equally marked. The essential part 

 of each luminous organ is always a collection of gland cells, 

 usually disposed so as to form the lining of a series of radially 

 arranged gland-tubules in the deeper part of the organ, which 

 also contains ganglion cells, and is supplied with nerves from 

 contiguous spinal or cranial nerves. The simplest form of phos- 

 phorescent organ consists of little more than these essential 

 elements. In the more complex organs an investing pigment- 

 sheath, reflecting 

 and lens-like struc- 

 tures, and an iris 

 diaphragm, either 

 singly or in com- 

 bination, may be FIG. 97. Opostomias micripnus. 

 flrlrlprl "Fia Q>7 phosphorescent organ, 



aaaea. Ig. y t Lendenfeld.) 



represents one of 



the simplest types of phosphorescent organ, which, in groups of 



1 Hoseley, Challenger Reports, Zool. xxii. 1887, p. 267. 



2 C. W. Wilson, Journ. Morph. xv. 1899, p. 667. 

 3 Burckhardt, Ann. Mag. Nat. Hist. (7), vi. 1900, p. 568. * Ibid. op. cit. p. 558. 



Median section of a simple 

 g, Radial gland tubes. (After 



