REPORT ON THE DEEP-SEA FISHES. 281 



I. HISTORICAL INTRODUCTION. 



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

 to the recoUectiou of the reader the investigations on this subject published by 

 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 

 Chaxdiodns, Stomias, Scopehis, and Argyropelecus, and came to the conclusion that in 

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

 segmentally grouped eyes. Theii- structure is compared with that of the so-caUed com- 

 posite organs with a simple cornea. 



Ussow compares them directly with the ocellar segmentally 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 anguilliformis. 

 Stomias barhatus. 

 Chauliodus sloani. 



Chatdiodtis setinotus. 



Scopdus rtssoi. 



Maurolicus am,ethystina-punctatus. 



Gonostoma denudatum. 



A rgyropelecus liemigymnus. 



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

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

 head, which I call glandular organs. He comes to the conclusion that those which are 

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

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



The more complicated organs, which 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 



1 R. Leuukart, Ueber mutlimassUche Xelienaugen bei eineni Fische, lieruht U. d. Versamml. deuUch. Naturf., 18(54. 



2 M. Ussow, Arbeiten d. Gesellsch. d. Naturf. St. Petersb., Bd. v. p. 70, 1874. 



3 According to G. O. Sars (Report on the Scliizopoda collected by H.JI.S. Clialleuger, Zool. Cliall. E\\>., part 

 xxxvii.) these are not eyes but phosphorescent organs. 



4 M. Ussow, Ueber den Ban der sogenannten angenahnlicheu Flecken einiger Knochenfische, Bull. Sac. imp. den 

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



(zool. ch.aj.l. EXP. — PART Mil. — 1887.) Lll 36 



