TYPES OF VERTEBRATE AND INVERTEBRATE EYES 23 



tissue, and the existence of a structural basis for the transmission of 

 impulses from sensory epithelial cells by afferent nerves to the central 

 nervous system. The existence of such close structural resemblances in 

 organs which are not truly homologous may serve the purpose of putting 

 us on our guard against drawing conclusions which are seen to be un- 

 warranted when all relevant circumstances are taken into account. 



Good examples of such structures are the " luminous organs " seen 

 on the ventro-lateral aspect of certain deep-sea teleosteans, e.g. Stomias 

 boa (Fig. 17) and the " photospheria " on the thoracic and abdominal 

 appendages of Nyctiphanes Norwegica, a crustacean closely allied to the 

 cuttle-fishes. An interesting point in connection with these " photo- 

 spheria," Fig. 18, ' is that in addition to the thoracic and abdominal 

 luminous organs, a pair which are similar in structure to these have been 



Fig. 17. — Stomias Boa — a Deep-sea Telostean Fish which is characterized 

 by a Series of Luminous Organs arranged in Longitudinal Rows along 

 the Ventro-lateral Aspects of the Body. (From Hickson, after Filhol.) 



shown by Vallentin and Cunningham to be present in the adult animal at 

 the base of the stalk of each of the composite faceted eyes. Incidentally 

 the appearance of this luminous organ in close association with the faceted 

 eye suggests the possibility of the latter having been evolved as a modifica- 

 tion of the more simple type of organ which is situated at the base of the 

 stalk. 



Claus, 2 in an earlier paper on Euphausia Mulleria, a nearly allied species, 

 speaks of these organs as " accessory eyes " of which some are median 

 and unpaired, while others are lateral and paired. He described them as 

 ten small, globular, reddish organs, having a resemblance in many respects 



1 R. Vallentin and J. T. Cunningham, Q.J. Micro. Sc, 25, 319. 



2 Claus, " Ueber einige Schizopoden und niedere Malacostraken, Messinas " 

 (1863), Zeit.f. zviss. Zoo!., 13. 



