404 



ARTHROPODA. 



behind this, in turn, the retina, consisting of cells which, at the 

 one end, bear < rods ' (4 and 7), at the other pass into nerve fibres. 

 The retina and vitreous body, surrounded by pigment, form a 



456 7 



FIG. 406. Diagrammatic section through anterior (A) and posterior (B) eyes of Epeira 

 diademat*,. (After Grenacher.) The hinder eye shows the inverted retina; 1, 

 lens ; 2, vitreous body ; #, epidermis, outside this, chitinous layer ; A, rhabdomes ; 

 5, retinal cells ; 6, capsule of eye ; 7, rhabdomes of inverted eye. 



spherical thickening sharply marked off from the rest of the epi- 

 thelium. These eyes, like those of vertebrates, must form inverted 

 images. 



In many spider eyes there is an inversion recalling that of the verte- 

 brates (fig. 406, B), the rhabdorae lying behind the nuclear portion of the 

 cell. Behind the rhabdomes comes a layer of strongly iridescent cells, the 

 tapetum lucidum. 



FIG. 407. Head of drone bee (After Swammerdam, from Hatschek.) Showing the 

 large faceted eyes and between them three ocelli. 



The compound eyes are much larger. They owe their name 

 * faceted eyes ' to the fact that the cuticle over them is divided 

 into polygonal (usually hexagonal) areas or facets (fig. 407). Each 



