CHAPTER 4 



EYES OF INVERTEBRATES 



Ccelenterates 



The simplest type of sense-organ which has been proved experimentally 

 to be sensitive to light is represented by the eye-spots or " ocelli " situated 

 between the bases of some of the tentacles in certain forms of Medusae, 

 e.g. the jelly-fish, Aurelia aurita (Fig. 52, A). They consist of specialized 

 groups of ectoderm cells containing red or black pigment, which are 



rc.c 



Fig. 52. — Diagram showing the Position of the Eye-spots of a Jelly Fish, 



Aurelia aurita. 



A — Side view. A segment of the umbrella has been cut away to show the interior. 

 B — A small part of the edge of the umbrella to show the position of the tentaculo- 



cyst and marginal lappets. 

 C — Vertical meridional section showing the position of the eye-spot. 



[Continued at foot of next page. 



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