16 THE ZOOLOGIST. 



(Ex. Stomias). 4th. Large, rounded, and flattened perlaceous 

 organs distributed on the sides of the body inferiorly, on the 

 head, operculum, and sides of the base of the tail (Argyropelecus) . 

 5th. Spots of a white glandular substance, which may be, in the 

 various species, on the sides of the body, on the dorsal or ventral 

 surface of the tail-peduncle, near the clavicles on the branchial 

 cavities, on the infra-orbital region of the maxillaries, on the 

 summit of the muzzle in front of the eyes, on the barbels, and 

 on the fin-rays. 6th. In this group the associated glands form 

 bands in the infra-orbital region (Idiacanthus). 7th. The photo- 

 genic apparatus of the dorsal fin is differentiated, having the 

 form of a cavity with an orifice and a filament (Ceratias). 8th. 

 The diamond-shaped organs form a single row on the scales of 

 the lateral line, and on the inferior branches of the muciparous 

 canals of the head. They are situated beneath the semitrans- 

 parent integument, but are independent of it (Halosaurus). 9th. 

 Two symmetrical photogenic organs lie on the snout to the right 

 and left of the median line — from the nasal cavities to the pos- 

 terior of the cranial cavity (Inops) . 



Like some previous authors, DeKerville is of opinion that 

 such fishes play a considerable part in the illumination of the 

 abysses of the ocean, and that the varied distribution of the 

 photogenic organs proves that the production of the light is 

 dependent on the uses to which it is applied. Thus he makes 

 two groups : — a. Those which have the general luminosity for 

 pointing them out to others which seek them as prey, the light 

 probably ceasing during repose. Those with brightly luminous 

 organs on the head near the eyes use it, he thinks, for searching 

 out their prey. b. The second group includes those in which 

 the photogenic organs are situated on fin-rays or tentacles, 

 apparently for the purpose of attracting animals to serve as food, 

 since it is well known that marine animals are attracted by light. 

 Moreover, this arrangement occurs in certain fishes with the eyes 

 little developed. When the organs are on the tail they also 

 attract prey, which is thus brought within reach of the agile pos- 

 sessors (such as the Scopelidce and Sternoptychidce). It can hardly 

 be urged that these luminous organs intimidate their enemies. 

 The notion of Perrier that the eyes of certain abyssal fishes are 

 phosphorescent he regards as doubtful. 



