Luminous Organs of Selachian Fishes. ."iG.i 



r will now proceed to tlie (loscilption of tho topographical 

 distribution of these photogenic organs, concerning which it 

 should be said that it dilFers in every species. 



In the genus Spinax these organs were discernible, besides 

 in S. niger, in S. pusillus i\\\(\ S. granulosus, oi \\\\\q,\\ latter the 

 type is {.ireserved in the British Museum, in pusillus they are 

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

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

 them, whereas on the iip[)erside they are very widely dispersed 

 or isolated. 



On examiinng 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 distributioji of these organs in Ltemargus rostratus is 

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

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

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

 as described by Joliann to exist on the corresponding portion 

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

 buted in irregular swarms, resembling small stripes, which 

 are j)laced 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 lino. 



Their distribution in lAvmargus burcalis is similar; but 

 whereas 125 of these structures can be counted on one side 

 of L. rostratus, in L. borealis their number is V5 only. On 

 com|)aring their distribution in the two species the following 

 are the principal ditl'erences in borealis : — 



The number of occipital organs is fewer. The prieJursal 



