Luminous Organs of Selachian Fishes. 563 



I will now proceed to the description of the topographical 

 distribution of these photogenic organs, concerning which it 

 should be said that it differs in every species. 



In the genus ftpinax these organs were discernible, besides 

 in S. niger, in S.pusillus and S. granulosus, of which latter the 

 type is preserved in the British Museum, [npusillus they are 

 distributed in an almost identical manner to those in S. niger, 

 i. e. the whole of the black under surface is densely beset with 

 them, whereas on the upperside they are very widely dispersed 

 or isolated. 



On examining several specimens I was greatly im- 

 pressed with the fact that these organs appear extremely 

 varied in point of distinctness, variations which are clearly 

 attributable to the amount of pigmentation consequent upon 

 the more or less fresh condition the specimens were in at the 

 time they were preserved. 



Up to the present time no phosphorescent organs were 

 known to exist in the genus Lcemargus, although L. borealis 

 has been known for many years and is a common inhabitant 

 of the Northern Seas. 



The distribution of these organs in Lcemargm rostrutus is 

 as follows: — On both sides of the head and immediately 

 in front of the opercles are two bands which seem to agree 

 with the posterior crura of a circlet consisting of these organs, 

 as described by Johann to exist on the corresponding portion 

 of the head in tipinax. The remaining bands are distri- 

 buted in irregular swarms, resembling small stripes, which 

 are placed transversely. Accumulations of this kind are 

 situated on the occipital region and also on the base of the 

 anterior dorsal fin orally. Moreover, an irregular row of 

 these organs runs along the body, beginning at the back of 

 the head and ending at the root of the caudal fin a short 

 distance from and above the lateral line. Lastly, there is a 

 short row, composed of seven of these organs, situated below 

 the hindmost gill opening, which converges, together with 

 the one on the other side, towards the ventral median line. 

 Excepting these latter, 1 have not discovered any more of 

 these structures below the lateral line. 



Their distribution in Lcemargus borealis is similar; but 

 whereas 125 of these structures can be counted on one side 

 of L. rostratus, in L. borealis their number is 95 only. On 

 comparing their distribution in the two species the following 

 are the principal differences in borealis : — 



The number of occipital organs is fewer. The praedorsal 



