xviii LIST OF ILIiUSTRATIONS. 



FIGURE 



TAGE 



pigmented epithelium; c?,the 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 ; h, 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 ; p, 

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



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



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

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

 fibres ; M, if, cross sections of ditto ; St, rods ; Pg, PS pig- 

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

 of the retina; Zif, crystalline cones; Et, retina; iVop, 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 ; n.c, nuclei ; n.c.s., nerve-cell 

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

 pseudocone; pg, pigment cells; p.op, perioptic ganglion; r, re- 

 tinula ; Hh, rhabdom ; T, trachea ; t.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?m, rhabdom .. .. .. .. 150 



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



ment cell ; rl, retinula ; i^m, rhabdom . . . . . . 152 



104. Eyelet of cockchafer. ?/, 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 ; 



wS cells of the retinula ; Rl, retinula ; Pm, rhabdom ; Cp, 

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

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

 3f, muscles for the movement of the eye-stalk ; Km, nuclei . . 157 



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



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



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



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



