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TEXT-BOOK OF ENTOMOLOGY 



way there arises out of the pit-like rudiment a two-layered 

 optic cup. The outer or superficial layer (I) becomes in its cen- 

 tral part the crystalline lens, while the peripheral parts form the 

 iris. From the cuticular striated border of these cells arise the 

 chitinous or corneal lens. On its outer edge the superficial layer of 

 the eye passes gradually into the unmodified hypodermis (/t). 



The inner, deeper layer of 

 the eye, which forms the con- 

 tracted cup - shaped portion, 

 appears to be the rudimentary 

 retina (/). From its cuticular 

 rod-like or fibrous edge arise 



FIG. 542. 



FIG. 543. 



FIG. 542. Two stages of development of the 5th of the six ocelli of larva of Acilius : c, cuticular 

 striated band ; el, germ destined to form the corneal lens ; ft, hypodermis ; /, crystalline-lens layer ; 

 n, optic nerve ; r, retinal germ ; sp, vertical fissure of the retina ; ar, the retina-cells bordering this 

 fissure. 



FIG. 543. Two later stages of development of the same eye as in Fig. 542 : i, iris ; m, middle 

 Inverted layer of the eye ; r, retina ; sp, vertical fissure of the" retina ; at, rods ; other letters as in 

 Fig. 542. This and Fig. 542 after Patten, from Korschelt and Heider. 



the visual rods. There soon arise certain peculiarities characteristic 

 of the eye of Acilius, i.e. the fissure (sp) bordered by the horizon- 

 tally situated rods of the large retina-cells (x). 



In the farther developed eye (Fig. 543) there is a flattening of the 

 cup-shaped inner edge, by which the bottom of the eye is levelled 

 and the little rods belonging to it stand up vertically (Fig. 543, 

 B, st). Then the cells belonging to the edge of the retinal cup (m) 



