VI PHOSPHORESCENT ORGANS AND EYES WAS 
number and long, the corneal lenses are highly arched, and the 
pigment is reduced to a few clumps in the iris. This part of the 
eve is evidently adapted for forming a vague superposition-image 
in the dusk. The ventro-lateral part (B), on the other hand, is 
composed of numerous small ommatidia, the crystalline cones of 
which can be completely iso- 
lated from one another by 
the irido-pigment. Immedi- 
ately below this part of the 
eye is a phosphorescent organ 
(C) provided with a lens and 
tapetum. Chun suggests that 
the ventro-lateral part of the 
eye is used for obtaining a 
clear mosaic image of objects 
illuminated by the phos- 
phorescent organ, while the 
frontal part of the eye is 
used for obtaining general 
visual impressions in dimly Fic. 104.—Section of eye of Stylocheiron masti- 
lit regions. hia’ carous gophorum. A, Frontal portion; B, ventro- 
lateral portion; C, phosphorescent organ ; 
differentiation of the eye D, entrance of optic nerve ; c, corneal lens ; 
: cr, crystalline cone; pg, pigment; ref, 
into two parts apparently retinula ; 7h, rhabdom. (After Chun.) 
only occurs in predaceous 
animals, which capture their prey alive upon the bottom, and to 
whom a clear vision of moving organisms is a necessity. 
Another instance of Crustaceans making use of their own 
light is given by Alcock,’ who found two deep-sea prawns, Hetero- 
carpus alphonst and Aristaeus coruscans, at about 500 fathoms in 
the Indian Ocean. These animals produce a highly phosphor- 
escent substance which they eject from the antennary glands, and 
they possess very large, deeply-pigmented eyes. 
The whole subject of the modification of the pigment and 
structure of Crustacean eyes is an interesting one, because it 
presents us with one of those cases in which the direct response 
to a stimulus acting within the lifetime of the individual seems 
to run parallel to the fixed adaptations of a whole species, which 
have become hereditary and apparently independent of the 
external stimulus of light or of the absence of hght. As far 
1 Loe. cit. p. 150. 
