PHOTOSPHERIA OF NYCTIPHANES NORVEGICA. 321 



it held the position of a choroidea with regard to the trans- 

 parent nucleated sphere. Claus could say nothing as to the 

 significance of the transparent layer with its bundle of rods, 

 but believed it to be the percipient element, although he could 

 not trace any relation between it and nerves. 



The pair of similar organs which are present behind the 

 facetted cornea in the eye- stalks in the adult, escaped Claus's 

 notice; but in the young larvae he mentions a bundle of rods 

 behind each eye, which were obviously the anterior pair at an 

 early stage of developmeut, though he did not recognise the 

 identity. Indeed, he was not likely to do so, for he could not 

 have expected to find an accessory eye in immediate contact 

 with the principal eye. 



His description is illustrated by small figures which are 

 drawn from the appearance of the organ in the fresh state in 

 situ, and accordingly do not adequately exhibit the minute 

 structure. 



The species Nyctophanes norvegica, on which our ob- 

 servations were exclusively made, was first defined by Michael 

 Sars in 1863 1 as Thysanopoda norvegica, and his diagnosis 

 of the red spherical organs agrees exactly with the account 

 given of them by Claus in ' Euphausia Miilleri:' " Organa 

 in ventre existunt octo sensitiva (haud dubie oculi simplices) 

 sphserica, cornea transparente semiglobosa, cseterum laete 

 purpure pigmentata, intus lente discreta crystallina len- 

 ticulari." 



It is surprising that in the numerous works published between 

 1840 and 1880, in which species belonging to the Euphausiidte 

 are described aud their accessory eves mentioned, no allusion 

 is made to any emanation of light from the animals, or to the 

 possibility that the supposed additional eyes are really phos- 

 phorescent organs, notwithstanding the fact that J. Vaughan 

 Thomson, long before 1840, described his discovery of a 

 Schizopod which was brilliantly luminous. The third memoir 

 of that author's zoological researches is entitled, " On the 



' Om Slaegten Tliysanopoda, og dens Norske Arter,' Christiania Vidensk 

 Forh., 1863. 



