PHOSPHORESCENT ORGANS. 187 



t 



usually enclosed in canals, bat they may be unenclosed and only 

 protected by flaps of skin {Batrachus, Lophius, etc). Their 

 distribution, whether they are enclosed or not, resembles that 

 found in Elasmobranchs and is indicated on Fig. 42. When 

 they are enclosed in canals, the tubes which leave the canal and 

 open on the surface are simple, ending in a single external pore ; 

 or they branch considerably before reaching the surface and oj^en 

 by several pores. The trunk part of the lateral line canal is 

 placed in the dermis and is usually without osseous supports, 

 but on the head the canals are either enclosed in small bones 

 which lie outside the skull bones, or they burrow in and are 

 protected by the bones of the skull andvisceral arches themselves. 

 There may be accessory lateral lines in the trwik, placed on 

 the sides of the body near the dorsal and ventral middle lines. 

 There are no ampullary canals. 



Many deep-sea fishes possess numerous shining bodies in the 

 skin resembling in their general features eyes.* It appears 

 probable that they are phosphorescent organs. They are 

 found either on the head near the eyes, on the lower 

 jaw, at the end of barbels, under the gill-cover, or in 

 rows in which they may be segmentally arranged along 

 the sides of the body, and sometimes in connection with 

 the lateral line. They vary considerably in structure from 

 being simply glandular patches of the skin which are supposed 

 to secrete a phosphorescent mucus to a state in which they 

 are more eyelike in appearance and possess a lens-like body 

 which, it is suggested, acts like the lens of a bull's-eye lantern in 

 concentrating the rays proceeding from the internal parts of the 

 organ. In the latter case a kind of tapetum can often be made 

 out at the back of the organ which appears to act as a reflector. 

 They are probably in all cases modified skin glands. It appears 

 probable that in many cases these organs are for the purpose 

 of enabling their possessors, which are generally provided with 

 large eyes, to see in the dark abysses of the ocean, but in some 

 cases no doubt they act as lures (when placed at the end of 

 barbels or far back on the body). In the case of Ipnops in which 



* F. Leydig, Die augendhnlichen Organe der Fische. Bonn, 1881. 

 M. Ussow, Ueber d. Bau der sogennanten augenahnlichen Flecken etc., 

 Bull. Soc. Nat. de Moscou, 1879. A. Giinther, Deep-Sea Fishes, in Chal- 

 lenger Reports, 22, 1887, and appendices by H. N. Moseley and R. v. 

 Lendenfeld. 



