xviii LIST or ILLUSTEATIONS. 



FIGURE PAGE 



pigmented epithelium; d,th.e lining epithelium of the mantle; 

 e, the lens ; /, the ligament supporting the lens ; g, the 

 retina ; A, the tapetum ; k, the pigment ; m, the retinal 

 nerve ; n, complementary nerve . . . . . . . . 143 



98. Schematic representation of the soft and some of the hard parts 



in a shell of a Chiton (Acanthopleura), as seen in a section 

 vertical to the surface, and with the margin of the shell lying 

 in the direction of the left side of the drawing, a, Conical 

 termination of sense-organ ; b, b', ends of nerve ; c, nerve ; /, 

 calcareous cornea ; g, lens ; h, iris ; k, pigmented capsule of 

 eye; m, body of sense-organ cut across; n, nerve of eye ; ^9, 

 nerve of sense-organ ; r, rods of retina .. .. .. 145 



99. Long section through the front (A) and hinder (B) dorsal eyes 



of Epeira diadema. A, Anterior eye ; B, posterior eye ; Hp, 

 hypoderm ; Ct, cuticle ; ci, boundary membrane ; M, muscular 

 fibres ; Ji, ilf , cross sections of ditto ; St, rods ; Pg, P^, pig- 

 ment cells ; L, lens ; Gk^, vitreous body ; K, nuclei of the cells 

 of the retina; Ajf, crystalline cones; Bt, retina; iVbp, optic nerve 147 



100. Section through the eye of a cockchafer (Melolontha). . .. 148 



101. Section through the eye of a fly. 6.m, Basilar membrane ; c, 



cuticle ; e.op, epioptic ganglion ; ii.c, nuclei ; n.c.s., nerve-cell 

 sheath ; N.f, decussating nerve-fibres ; op, optic ganglion ; pc, 

 pseudocone; j^g, pigment cells; p.op, perioptic ganglion; r, re- 

 tinula; i?A, rhabdom; T, trachea; ^.a, terminal anastomosis ; 

 Tt, trachea ; ti, tracheal vesicle . . . . . . . . 149 



102. Two separate elements of the faceted eye of a bee. Lf, Cornea ; 



n, nucleus of Semper ; Kk, crystalline cone ; Pg, Pg^, pigment 

 cells; i?/, retinula ; i?Hi, rhabdom .. .. .. ..150 



103. Eyelet of cockroach. If, Cornea ; kk, crystalline cone ; pg', pig- 



ment cell ; rl, retinula ; nn, rhabdom . . . . , . 152 



104. Eyelet of cockchafer. If, Cornea ; kk, crystalline cone ; pg,pg', 



pigment cells ; W, retinula; rm, rhabdom .. .. .. 152 



105. Leptodora hyalina . . . . . . . . . . . . 156 



106. Eye of Mysis. n. Nuclei ; Lf, facets ; Kk, crystalline cones ; 



n^, cells of the retinula ; El, retinula ; Bm, rhabdom ; Cp, 

 blood-vessels; N, fibres of the optic nerve ; iV", iV"^, N^^^^, 

 decussations of the fibres of the optic nerve ; G, G^, ganglia ; 

 M, muscles for the movement of the eye-stalk ; Kiyi, nuclei . . 157 



107. Corycaeus. a, b, The eye . . . . 158 



108. Eyes of Calanella Mediterranea. Pg, pigment cells ; N.fr, 



frontal nerves ; N.op, nervus opticus. The numbers show 



the numbers of the cells . . . . . . . . . . 159 



