LIST OF ILLUSTEATIONS. xix 



FIGURE 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 retinulae. a, Cuticle ; bb, cuticular lens ; 

 cc, hypoderm; i??i, retinula ; n, nerves .. .. .. 160 



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



111. Luminous organ of i7M^AaMSi"a. /, Fibres; e, lens .. .. 162 



112. Eye-stalk o{ Ficphausia. lo. Luminous organ ; a, lower eye . . 162 



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



X, position of the image ; s, rod ; sc, sheath ; scm, outer 

 sheath ; r, retina ; y, 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 ; k, 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; 6, brain; e, eye; h, heart; m, 



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

 s, stomach ; y, three eggs deposited in the space between the 

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



