PHOTOSPHERIA OP NYCTIPHANES NORVEGICA. 325 



on the body leaves nothing to be added ; it is necessary here 

 simply to indicate their position briefly. The organ in the eye 

 peduncle is dorsal to and somewhat on the outer side of the 

 eye, and in close contact with the latter. The thoracic organs 

 are contained in the coxal segments of their respective limbs ; 

 the anterior pair are on the internal side of the limb, and cannot 

 be seen in the ordinary condition and position of the animal ; 

 they are directed downward and inward when the animal is on 

 its ventral surface. The posterior pair are on the external side 

 of the limb, and are directed downward, outward, and backward. 

 This pair are quite conspicuous in the living animal, and in the 

 dead specimen without any operation being performed on it. 

 The abdominal organs are simply directed downwards. 



The position of the organs is constant throughout all the 

 genera of Euphausiidae with two exceptions. In Stylocheiron 

 there are only five, one ocular pair, the posterior thoracic pair, 

 which have an additional lens, and a single caudal organ. In 

 Bentheuphausia, which is the only one brought up by the 

 " Challenger " from deep water (1000 — 1800 fathoms), accord- 

 ing to Sars there are no luminous organs and the eyes are 

 imperfectly developed, while Willemoes Soehm believed that 

 organs he found on each of the thoracic limbs were the 

 luminous organs. 



We have examined, at Mr. Murray's suggestion, the struc- 

 ture of the luminous organs, or as they may more conveniently 

 be called, photospheria, of Nyctiphanes norvegica, G. O. 

 Sars. Before proceeding to describe the result of our studies 

 we will say a few words as to the distribution of the species. 

 It is a distinctly northern form, being absent from the Mediter- 

 ranean and the warmer parts of the Atlantic. It is abundant 

 on the west coast of Norway, having, as we have already men- 

 tioned, been first defined from Norwegian specimens by M. Sars 

 under the name Thysanopoda norvegica. But in consi' 

 dering the localities where specimens have been taken, it is 

 necessary to mention whether the capture was made from the 

 surface waters or from the bottom. The adult, so far as our 

 information allows of a decision, lives on the bottom, and never 



