FISHES CHAP. 



mere mechanical laceration ; but, except the mucus secreted by 

 the gland cells of the skin, which may possess venomous pro- 

 perties, no special poison-forming glands in connexion with the 

 spines are at present known. 



Phosphorescent Organs. 1 



In common with many other animals of similar habitat, 

 phosphorescent organs (photophores) are highly characteristic 

 structures in many deep-sea Teleosts belonging to widely different 

 families (e.g. Stomiatidae, Scopelidae, Halosauridae, and Anoma- 

 lopidae). These organs probably had their origin in local aggre- 

 gations of the gland cells of the epidermis, which had acquired 

 the power of secreting a luminous slime. Luminous organs vary 

 greatly in number and in their mode of distribution in the skin. 

 Usually they are found on the sides and ventral surface of the 

 body and head, very rarely on the dorsal surface, and they often 

 present the appearance of brightly glistening jewels set in the 

 skin. A very frequent method of arrangement is in one or two 

 longitudinal lines along the lateral and ventral surfaces, sometimes 

 extending continuously from the head to the end of the tail (Fig. 

 371, A, and Fig. 379), but occasionally interrupted and limited to 

 portions of the body and tail ; and in a few a distinctly meta- 

 meric disposition is obvious. On the other hand, the very numerous 

 and simple organs of Opostomias are disposed in many transverse 

 bands along the sides of the Fish. In addition to these organs, 

 which are usually numerous, and whose arrangement is linear, 

 specially large and often structurally complex luminous organs are 

 present on different parts of the head and body. In Opostomias 

 micripnus there is a phosphorescent organ on a median barbel 

 depending from the chin. Sternoptyx diaphana has one on the 

 lower jaw. The presence of one or two organs beneath the eyes (Fig. 

 96) is characteristic of several species (e.g. Opostomias micripnus, 

 Astronesthes niger, Pachystomias microdon, Scopelus benoitii, Mala- 

 costeus indicus). Opostomias micripnus has a luminous organ on 

 the isolated and elongated first fin ray of the pectoral fin, while in 

 certain deep-sea Angler-Fishes (e.g. Ceratias) there is one on the 

 anterior cephalic fin-ray of the dorsal fin. The Scopelid Ipnops 



1 Lendenfeld, Chall. Reports, Zool. xxii. 1887, p. 277. For references to papers 

 by Leydig, Ussow, Emery, and others, see Lendenfeld, op. cit. 



