xvi List of Ilhistrations. 



FIG. PAGE 



31. THE HUMAN EYE . . . . . . . . . . . . 274 



32. EETINA OP THE EYE . . . . . . . . . . 274 



33. VARIATION IN THE LIMITS OF COLOUR-VISION . . . . 281 



34. PINEAL EYE . . . . '\ . . . . . . . 288 



35. SKULL OF MELANERPETON . . . . . . . . . . 288 



36. EYES AND EYELETS OF BEE . . . . . . . . 289 



37. EYE OF FLY . . . . . . . . . . . . 290 



38. DIAGRAM OF MOSAIC VISION .. .. .. .. 291 



39. DIRECTION-RETINA . . . . . . . . . . . . 295 



40. ANTENNARY STRUCTURES OF HYMENOPTERA . . . . 297 



