LIST OF ILLUSTRATIONS. XVll 



FIGURE PAGE 



82. Diagram of a section through the skull and pineal eye of Lacertu 



viridis. C, Cuticle ; Pa, parietal bone ; Ep, epidermis ; L, 

 lens ; Pig, Pigment ; E, rete mucosum ; CH, cerebral hemi- 

 sphere; iV", nerve ; ^, epiphysis ; (?/?Z, optic lobe of brain 128 



83. Englena viridis. e, Eye-spot . . . . . . . . . . 130 



84. Section through the simple eye of a young Dytiscus larva. I, 



Corneal lens ; g, cells forming the vitreous humor ; r, retina; 



0, optic nerve ; h, hypoderm . . . . . . . . . . 131 



85. Eye-spot of Lizzia. oc, Ocellus ; I, lens . , . . . . 132 



86. Eye-bulb of Astropecten 132 



87. Eye of Asteracanthion. c, Cuticle ; e, epithelium ; I, lens ; p, 



pigment . . . . . . . . . . . . . . . . 133 



88. Anterior extremity of a freshwater worm (Bohemilla comata). 



a, Eye; b, brain; c, cuticle; Iqy, hypoderm; lb, tactile hair; 



ne, nerve ; v, blood-vessel . . . . . . . . . . 135 



89. Eye-dot of Nereis. In B the pigment is partly removed so as 



to show the lens . . . . . . . . . . . . 135 



90. The first twelve segments of Polyophthalmus pictus, seen from 



below. The Roman numerals indicate the segments. St, 

 Papillae on the head ; KS, head ; au, head eye ; s.au, side eyes ; 



01, upper lip ; Ul, under lip ; v.ph, pharyngeal vein ; V.subinta, 

 anterior ventral vein ; V.d.l^-*, veins connecting the superior 

 lateral and vessels ; sept^-^, intersegmentary membranes ; 

 m.ocs.l, lateral muscle of the oesophagus ; V.ann, pulsating 

 circular vessel ; Md.dr, stomach-glands ; V.v-l, vein con- 

 necting the inferior and lateral blood-vessels ; 3Id, stomach ; 

 Bm, muscles of the hairs ; G, brain ; fl.o, ciliated organ ; qm, 

 transverse muscle ., .. .. .. .. .. 136 



91. Alciope 137 



92. Perpendicular section through the eye-pit of a limpet (Patella). 



1, Epithelial cells ; 2, retina cells ; 3, vitreous body . . 138 



93. Eye of Trochus magus. Gl, Vitx'eous body ; No, nerve . . 138 



94. Eye of Murex brandaris. L, Lens ; Gl, vitreous body ; No, nerve 139 



95. Eye of Helix pomatia. ct, Cuticle ; a, epithelium ; b, cornea ; 



c, envelope of the eye; d, cellular layer; e, fibrils of the optic 

 nerve ; /, feeler cell ; na, nerve of the tentacle ; no, optic 

 nerve . . . . . . . . . . . . . . . . 140 



96. Perpendicular section through an eye of Area noce. 1, Epithe- 



lium of the edge of the mantle ; 2, cells of vision ; 3, lens : 



4, 5, connective tissue ; 6, section of one of the cells . . 142 



97. Diagram of eye of Pecten. a, Cornea ; b, transparent basement 



membrane supporting the epithelial cells of cornea ; c, the 



