508 On the Luminous Organs oj Selachian Fishes. 



rather evenly distributed over the entire specimen, though 

 somewhat sparser perhaps when compared with forms pre- 

 viously mentioned. 



In fig. 7 I was obliged to have recourse to a restoration in 

 part after Centroscyllium Fabricii for the first dorsal and the 

 caudal fin, as well as for the distribution of the photogenic 

 organs, the skin of the specimen of C. granulosum having 

 sustained some damage. These organs are also present in 

 C. Fabricii, but unfortunately the specimen at my disposal 

 was likewise defective, a circumstance which entirely 

 hindered the study of the distribution of these structures in 

 this species. 



An oceanic Spinacid, Paracentroscyllium ornatum, which 

 has been described by Alcock, seems to be more closely 

 allied to Spinax than to CentroscyUium, to judge from the 

 description of its colours by this author. Only one of the 

 three specimens belonging to this species is in the British 

 Museum, and on this I found the organs of luminosity 

 present. 



They are relatively large in size, and are confined merely 

 to a few places — for instance, on the muscular portions of the 

 pectoral fins, then again on the two ventrals, and on both 

 dorsal ones. They further occur on the inferior lobe of the 

 caudal, consisting of a single row only, in smaller groups and 

 more widely diffused over and below the eyes. Dorsally they 

 make their appearance between the spiraculum and a little 

 beyond the ventral fin, over the whole of the gill-region, and 

 towards the anus on the ventral surface. 



It may here be remarked that I have searched in vain for 

 these photogenic organs in Centrophorus granulosus, C. cal- 

 ceus, C. squamosus, Scymmodon ringens, Scymnus lichia, Cen- 

 Irina, Notidanus, Echinorhinus, and Ghlamydoselache. 



In conclusion, it will be seen that organs of phosphorescence 

 exist in eleven species of Selachians, inclusive of Isistius 

 brasiliensis (Bennett) and of Spinax niger (Johann). 



In structural characters they are very similar, and exhibit 

 a primitive degree of development *. 



The distribution of luminous bodies is characteristic of the 

 respective genera and species. All Selachians which possess 

 them are pelagic, and they belong to the family Spinacidse 

 (Giinther) = lSpinacida3 + La3margidae of authors. 



* Luminous organs of a similar form Lave been described in a Teleo- 

 stean tish (" The Phosphorescent Organs in the Toad-fish, Poruhthys 

 notatus, Girard," by Cii. Wilson Green, Journ. of Morphol. vol. xv. 

 1899). With reference to this I may mention that I have also noticed 

 their existence in the occipital region of the haddock. 



