ART. 15. — II. OHSIIIMA I SOME OBSERVATIONS 



to each other, the hitter differing from the former only in 

 the form and arrangement of dermal denticles and in having a 

 milky white spot on the head, which, like the white crescent- 

 shaped spot at the jiosterodorsal margin of the eye, is due to 

 the presence of a subdermal cartilage, and is not a luminous or- 

 gan, as was supposed to be by Pietschmann. 



Topographical Distribution, 



One can distinguish two forms of photophores in Etmoptems, 

 viz. the punctate and the linear, as Johann has found in 

 Spinax niger. 



The distribution of the 

 photophores in the species 

 studied by me agrees so closely, 

 with that of 8pinax niger, that 

 I deem a detailed description 

 unnecessary. In E. fronti- 

 maculatus, in which the photo- 

 phores are less developed than 

 in lucifer, the postanal area 

 of photophores (Textfig. 1 B, 

 Pa) gives off posteriorly neither 

 a median nor lateral branches 

 as it does in lucifer (A, Px and 

 P2) ; or more properly speaking, 

 the three branches are united 

 to form a single broad area. 

 In correspondence with this, , , ^ a tm a ^ , ^ ^c v,^ 



I- ' second dorsal fin, Dl dorso-lateral row of pho- 



the caudal area of photophores tophores, Pa postanal area of photophores, Pi 



lateral posterior prolongation of the same, P-z 

 in E. frontimaculatus {C) are median posterior prolongation, Fc pelvic fins. 



Fig. 1. Postrior regions of (A) Eimopterus 

 lucifer and (B) E. fronlimaeulatus, showing the 

 distribution of photophore^. Oblique view of 

 tlie ventral side; tiie photophores are indicated 

 by dots and broken lines. X|. C caudal area of 

 photopliores, Ci posterior prolongation of the 

 caudal area, C^ solitary area on the tail fin, D 



