REPORT ON THE DEEP-SEA FISHES. 281 



I. HISTORICAL INTRODUCTION. 



Before entering into the results of this research it may be advantageous to luring 

 to the recollection of the reader the investigations on this subject published l)y 

 other authors. In doing so I shall strictly confine myself to the papers on the Histology 

 of these organs. 



The first who paid special attention to the histology of these organs was R. Leuckart,^ 

 who called them " accessorische Augen." 



Afterwards, Ussow^ published a short account of these organs. He examined 

 Chauliodus, Stomias, Scopelus, and Argyropelecuis, and came to the conclusion that in 

 these genera the organs in question were, as Leuckart had assumed, accessory and 

 segmcntally grouped eyes. Their structure is compared with that of the so-called com- 

 posite organs witli a simple cornea. 



Ussow compares them directly with the ocellar segmeutally distributed accessory 

 eyes of Euphausia? 



Afterwards, Ussow studied these structures in some other species, and published a 

 very detailed account'' of his researches, which were made on the organs of the following 

 species : — 



Astronesthes martensii. 

 Stomias ang uillifoi •mis. 

 Stomias harhatus. 

 Cliauliodus sloani. 



Chauliochis setinotns. 

 Scopelus rissoi. 



Ma u rolicus amethystina-punctatus. 

 Gonostoma denudatum. 

 Argyropelecus hemigymnus. 



It appears that he only examined those organs which are designated ocellar organs 

 in this Report. He did not extend his investigations to those found chiefly on the 

 liead, which I call glandular organs. He comes to the conclusion that those which ai-e 

 more simple in their structure arc glandular in function, although they have no external 

 opening. I can endorse Ussow's descriptions and figures of these organs. 



The more complicated organs, wliicli are incised near the middle, and which are 

 designated below as " composite ocellar," are considered by Ussow as eyes. 



His descriptions and figures of these are not in accordance with the results obtained 

 by Leydig and myself. 



• R. Leuckart, Ueber miithmassliche Nebenaugen bei einem Fische, Bericht ii. d. Vcrsamml. (kutsch. Naturf., 1864. 

 '■* M. Ussow, Arbeiten d. Gesellsch. d. Naturf. St. Petersk, Bd. v. p. 70, 1874. 



3 According to G. O. Sars (Report on the Seliizopoda collected by H.M.S. Challenger, Zool. Chall. E.\p., part 

 xxxvii.) these are not eyes but phosphorescent organs. 



* M. Ussow, Ueber den Ban der sogenannten angen.ahiilicheu Flecken einiger Knochenlische, Bull. Soc. imp. dcs 

 Nat. Moscou, t. liv. No. 1, p. 79, 1879. 



(zool. chall. e.xp. — PART Lvii. — 1887.) LIl 36 



