SECT. VI 



THE SENSORY ORGANS 



107 



fold as already described, the anterior pair followed 

 them, and also disappeared under the fold, but, 

 naturally, nearer the opening. While the paired eyes, 

 perhaps with the aid of the water lenses, remained 

 functional as eyes, the anterior pair of Annclidan eyes 

 seem to have been dragged out of their hypodermal 



FIG. 28. Diagram to show the origin of the unpaired eye out of two eye-spots, the 

 retinae being drawn down to form the lateral retinas of that organ. /, pigment 

 cells. The pigment in the eyes is not drawn. 



position, and to have been arranged so as together to 

 form the cavity already described. The hypodermis 

 cells can still be seen secreting the chitinous membrane 

 of the under side of the water-sac. The retinae now 

 forming the unpaired eye seem to be connected with 

 the original hypodermis only through fine connective 

 tissue and pigment strands, similar pigment cells also 



