102 



THE APODID^E 



PART I 



point very nearly abutting on the brain. The posterior 

 wall of the cavity and the posterior half of its floor 

 are also composed of somewhat similar retinae. The 



dr 







mmm^^ 





FIG. 25. Longitudinal median section through the unpaired "eye," diagrammatic. 

 vr, ventral ; dr, dorsal retina ; /, tangb of pigment cells ; s, -water-space over 

 the eyes ; c, canal of the same, giving off a branch (ci) into the interior of the 

 organ ; b, brain. 



sensory ends of all these retinal cells point inwards ; 

 the nerves from the outer ends of the cells unite 

 together to run towards the brain, forming from the 

 four rctinaj four nerve strands on which the un- 



