274 THE VOYAGE OF H.M.S. CHALLENGEE. 



layer of naiTow tniaspurent rods present in the accessory eye of Stomias onguilliformis 

 as figured by Ussow* (Tab. ii. fig. 10, h) ; but the component rods here, as in all allied 

 organs of fishes as yet described, have no hexagonal terminal nucleated cells attached 

 to their extremities. Moreover, the hexagonal cells (?) forming the layer beneath 

 the rods are in Stomias filled with iridescent rod bodies (" Flitterchen " of Leydig), 

 forming what Ussow, who holds the organs to be eyes, calls a tapetum ; whilst 

 in the case of the organs of Ipnops no such iridescent layer is present, but 

 only in its place a layer of hexagonal pigmented nucleated cells exactly like that 

 occupying a similar position in the corresponding organ of Chatih'odus sloani (Ussow, 

 loc. cit., Tab. ii. fig. 8). In this organ of Chauliodus, however, the rod-like bodies bear 

 scarcely any resemblance to those of Ipnoj)s, being immensely long, with one extremity 

 club-shaped and the other drawn out into a fine filament. A still more important 

 diSerencc is the absence of any trace of the lens-like bodies present in the organs both 

 of Chauliodus and Stomias. There seems to be no trace at all of the iridescent 

 structures in Ipnops. Leydig appears to question the accuracy of Ussow's determination 

 of the polygonal pigmented objects as cells in every instance,^ but there can be no doubt 

 that the bodies forming the layer beneath the rod layer in the organs of Ipnops are 

 cells, since they have a well-defined nucleus, which may be well stained with camiine. 

 On the whole, though the organs of l2)nops show to some extent corresponding structure to 

 the " augenahnliche Organen " of Leydig it is evidently rather with the two other groups of 

 his classification (Leydig, loc. ci<.,pp. 64, 70, 73), the " Glasperlen-iihnlichen Organe " and 

 the " Leuchtorgane," that they are most closely allied. The former are descriljed as slight 

 plate-like depressions of the outer skin surftice with a dome-like transparent roof, with the 

 following structure in all species. An outer brown pigmented capsule, a layer with a 

 metallic iridescence, a connective tissue gelatinous body, nerves and blood-vessels. In 

 many species there is present besides a spindle-shaped string or plate of homogeneous 

 granular constitution. 



The organ in Ipnops possesses the nerves though apparently not so richly developed, 

 tiie blood-vessels and the brown })igmentcd capsule, and a I'cpresentative of the layer 

 with the metallic; glance, in the hexagonal pigmented cells devoid of such glance. It has 

 no trace of a gelatinous body, but the spindle-shaped string or plate may be represented 

 in it by the rod layer. In the glass-bead-like organs of Scopelus nssoi, the i)latc shows 

 a striate arrangement of its component granules (Leydig, loc. cit., p. 45). 



Leydig examined the two pairs of phosphorescent organs on the head of Scojx'lvs 

 rftftiiesqidi, l)ut unfortunately for lack of material was unable to make out a complete 

 account of their histology ; he, however, convinced himself that their structure is 



' M. Ussow, Uirbcr licii Huu dcr sogenanntcn augenuhnliilu'ii KUikiMi finif,'er Knocheiifisclie, Bull. Soc. da 

 Naluralislea de Moscoit, 1879. 



^ Leydig, Die augeniilinlichcn Organe der Fiscbe, Bonn, 1881, pp. 71, 72. 



