Luminous Organs of Selachian Fiihes. 553 



which the skin of Spinas niqer is covered in great numbers, 

 more particularly so on its black-coloured parts. In addition 

 to describing their distribution upon the surface of the body 

 and their histological structure, which in the main points 

 corresponds with those of Phyllirhoe and the Pennatulidse, he 

 also compares them with other luminous organs. 



He moreover refers to a previous observation on phospho- 

 rescence made in another Spinacide species, Isistius bra- 

 siliensis, by Bennett as early as 1840 during a whale voyage, 

 in which he states expressly that, with the exception of a 

 ring on the throat remaining dark, the whole of the ventral 

 surface of this fish was aglow for about three hours. It 

 struck Johann as being remarkable, when he discovered on 

 the throat in Spinax two regions extending towards the median 

 line which were devoid of these structures. From this fact 

 alone, and quite apart from purely structural characters, he 

 was right in his surmise, that in all likelihood they would 

 have to be regarded as organs of luminosity. 



The accuracy of his notions as regards their functions was 

 moreover fully borne out in a note from Th. Beer, dated 

 Jan. 31, 1899, which reached Johann in time to find a 

 place at the end of his paper. 



In his note Beer says that, whilst engaged in ophthalmo- 

 scopic observations on Spinax in a room darkened for this 

 purpose, its phosphorescence was vivid enough to enable 

 him to see it at a distance of from 3-1 metres. " The whole 

 of the ventral surface of the animal," he continues, " from 

 the snout to the root of the tail, was glowing with a feebly 

 shining greenish lustre, as if it were impregnated with phos- 

 phorus or had been coated with a luminous paint, with this 

 difference, however, that luminosity appeared and disappeared 

 at short intervals, but invariably increased in intensity just 

 before its disappearance." 



In this wise Johann's interpretation was indisputably 

 confirmed. He further, too, more fully entered into those 

 questions of their physiology which are so closely connected 

 with these remarkable structures ; and he finally endeavoured 

 to supply proof of their presence in other Selachians which 

 he examined for this purpose, without, however, being able to 

 do so. 



The genera investigated by him with the aforesaid object 

 were : — Stegostoma, Carcharias, Scyllium, Pristiurus, Muste- 

 lus } Crossorhinus, Zygoma, Chimcera, Centruphorus (granu- 

 losus), Lozmargus {borealis), and Scymnus. 



At the time when Johann published his work I had already 

 noticed some peculiar structures in L&margus roslratus. a 



37* 



