I02 



THE APODID^ 



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 



Fig. 25.— Longitudinal mfdian section through the unpaired "eye," diagrammatic. 

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

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

 orsran ; h, 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 retinai four nerve strands on which the un- 



