LIST OF ILLUSTEATIONS. XlX 



FIGURR PAGE 



109. Diagram of a vertical section through a portion of the lateral 



eye of Limulus polyphemus, showing some of the conical lenses, 

 and corresponding retinulse. t^, Caticle ; 6&, cuticular lens ; 

 cc, hypoderm ; Mn, retinula ; /i, nerves . . . . . . 160 



110. Euphausia pelluoida. ?.o, Luminous organ .. .. ,. 161 



111. Luminous organ of ^M^Aawsi'a. /, Fibres ; tf, lens ., ,, 162 



112. Eye-stalk oi Euphausia. lo, Luminous organ ; a, lower eye . , 162 



113. One of the elements of the eye of a fly. kk. Crystalline cone; 



a;, position of the image ; 5, rod ; sc, sheath ; scm^ outer 

 sheath; r, retina ; j/, seat of vision .. .. .. .. 166 



114. Photichthys argenteus .. .. .. .. .. .. 185 



115. Ceratius bispinosus . . . . . . . . . . . . 186 



116. Edge of a portion of the mantle of Aglaura hemistoma, with a 



pair of sense-organs, v, Velum; h, sense-organ; ro, layer of 

 nettle cells ; t, tentacle . . . . . . . . . . 188 



117. Sense-organ of leech. 1, Epithelium ; 2, pigment ; 3, cells ; 



4, nerve . . . . . . . . . . . . • . • • 189 



118. Daphnia pulex. a, Antennae ; h, brain ; e, eye ; h, heart ; m, 



muscle of eye ; «, nerve of eye ; o, ovary ; ol, olfactory organ ; 

 .I, stomach; y, three eggs deposited in the. space between the 

 back and the shell , . . . . ■ . ■ . • • • 211 



