THE EYE 147 



lines crossing each other nearly at right angles, 

 each facet corresponding to one of the elements of 

 which the compound eye consists. 



b. Structure of the eye as seen in a longitudinal 



section. 



Car ef idly divide the eye-stalk and eye longitudinally into 

 two halves. The calcified portion of the cuticle is best cut 

 with scissors, the remainder with a sharp knife. Examine 

 one of the cut surfaces with a strong lens. 



The eye consists of a number of conical 

 bodies arranged in a radiate fashion, their bases 

 being turned outwards and formed by the corneal 

 facets, and their apices being directed inwards 

 and connected with the optic ganglion. Each of 

 these component elements is a complete eye in 

 itself, and is isolated optically from its neighbours 

 by pigment. 



i. The cornea is thin and semicircular in section, 

 and the strips of cuticle separating its facets 

 scarcely differ from the facets themselves. 



ii. The crystalline pyramids are transparent 

 conical bodies arranged radially and abutting 

 upon the cornea, each pyramid corresponding 

 to one corneal facet. They are separated 

 from one another by layers of pigment near 

 their outer ends. 



iii. The inner ends of the pyramids are imbedded 

 in a black pigmented layer, in which lie a 

 series of rods and fusiform bodies, each of the 

 latter being surrounded by a layer of brilliant 

 pigment, either white or pink. 



iv. The optic ganglion occupies the centre of the 

 eye. Its surface is deeply pigmented. 



V. The optic nerve lies in the axis of the eye-stalk, 

 and connects the optic ganglion with the 

 * brain.' 



L2 



