VI PHOSPHORESCENT ORGANS 179 
murrayt' (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 benoitiz) 
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.” 
Fic. 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).2 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 Selachu 
(Spinacidae), of which some are known to be luminous.* 
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 Fic. 97.—Opostomias micripnus. Median section of a simple 
. phosphorescent organ. g, Radial gland tubes. (After 
added. Fig. 97 Lendenfeld.) 
represents one of 
the simplest types of phosphorescent organ, which, in groups of 
1 Moseley, Challenger Reports, Zool. xxii. 1887, p. 267. 
2 ¢. W. Wilson, Journ. Morph. xv. 1899, p. 667. 
3 Burckhardt, Ann. Mag. Nat. Hist. (7), vi. 1900, p. 568. 4 Ibid. op. cit. p. 558. 
