330 



INSECTA. 



approaches this common type the most nearly, and we shall therefore 

 content ourselves by describing its development alone. 



The rudiment of this ocellus (Fig. 162 A), at a certain stage of its 

 development, strikingly recalls the simple optic pits or cup-shaped 



Fig. 163. — Two later stages in the development of the fifth ocellus of the Acilius larva (after 

 Patten), cl, chitinous lens ; i, so-called pigmented iris ; 1, lentigen layer (vitreous body) ; 

 m, middle inverted layer of the eye ; r, retina ; sp, vertical slit in the retina ; st, rods ; 

 x, cells bordering the vertical slit. 



