324 RUPERT VALLBNTIN AND J. T. CUNNINGHAM. 



the organ, which, moreover, in fresh specimens is coated with a 

 beautiful red pigment in its posterior half, whereas the front 

 portion remains quite pellucid. On closer examination the 

 two portions are found to fit as it were into each other without 

 being actually connate. At the junction a glistening ring may 

 be seen internally, encompassing in the middle a highly refrac- 

 tive lenticular corpuscle. The posterior hemisphere is filled 

 up with cellular matter, in the midst of which lies embedded a 

 flabelliform bunch of exceedingly delicate fibres, exhibiting 

 in fresh specimens a most beautiful iridescent 

 lustre. " To the equatorial zone of the organ, moreover, two 

 or three thin muscles are attached, admitting to a certain 

 extent of its being rolled to and fro." 



Sars then refers to the observation of J. Vaughan Thompson 1 

 that these Crustacea are highly luminous at night, and states 

 that he himself has observed their luminosity in the Norwegian 

 species, doubtless principally in Nyctiphanes norvegica 

 and he found that the animal was able by varying the 

 movements of the organs to increase or diminish the light 

 at will. He believed that the chief light-producing matter was 

 the fibrous fascicle lying in the centre of the organ. " Even if 

 the organ be crushed and this fascicle be extracted it still con- 

 tinues to give forth a comparatively strong phosphorescent 

 light when seen in the dark." The lens he believes to act as a 

 condensor for the light, and the pigment coating behind to 

 prevent the light being radiated in all directions. He gives 

 four reasons which show that the organs are not eyes ; (1) that 

 the nerve to the organs is very thin and does not give rise to 

 any special retinal expansion ; (2) that the structure of the 

 posterior portion of the organ is not that of an eye ; (3) that 

 the position of the organs is ill adapted for vision, and (4) the 

 presence of one of the organs in the eye peduncle. 



He points out that the ocular organ is immobile, and entirely 

 lacks the front hemisphere with its lens, and that the light from 

 it is more intense and more steady than that from the others. 



Professor Sars's description of the position of the organs 

 1 Quoted by mistake as W. Thomson. 



