362 



THE LOCUST 



plan similar to that of a vertebrate. The form of the lens is 

 unchangeable, as is also the distance between the lens and the 

 retina. There is, therefore, no possibility of adjusting the focal 



,-. s 



^ --^- h 



Fig. 1S3. — Eyes of arthroiDods. 



A, compound eye of crayfish in longitudinal section showing the numerous ommatidia. 

 B, two ommatidia of crayfish showing details of structure. C, ocellus or simple eye of 

 honey-bee in longitudinal section. c, corneal facet or external surface of ommatidium; 

 c.h., hypodermis cells of facet; c.i., crystalline cone, proximal part; c.o., crystalline 

 cone, distal part; f.o., fibers of optic nerve; h, hypodermis; m, muscle; m.b., basal mem- 

 brane; n.c, nucleus of cornea cell; n.d. and n.p., nuclei of retinal cells; om, ommatidium; 

 p.i., pigment of iris; pg.b., pg.d., and pg.p., pigment; r, retinal cells; rh, rhabdome; s, skel- 

 eton; V, vitreous body. (A and B redrawn from Howes, "Atlas of Zootomy," copyright, 

 1902, Macmillan & Co., Ltd., printed by permission; C, redrawn from Folsom, "Ento- 

 mology," copyright, 1906, by P. Blakiston's Son & Co., printed by permission.) 



" seen " must be at a fixed dis- 



plane, and hence an object to be 



tance. As the lens is usually very convex, the focal distance must 



be short and the vision by ocelli correspondingly near-sighted. 



