CONTENTS. IX 



of Crustacea— Structure of eye— Mysis— Corycseus— Copilia 

 —Calanella—Limulus—ScorpioDS— Light-organs of Eu- 

 pliausia— Mode of vision by compound eyes— Muller's theory 

 of Mosaic vision— Images thrown by the cornea — Objections 

 to other theories— Position of the image— Absence of power 

 of accommodation — Absence of retina — Summary — On the 

 power of vision in insects — Experiments on vision of insects 

 —On the function of ocelli— Difficulty of subject— Experi- 

 ments— Short sight of ocelli— Ocelli of cave- dwelling spiders 

 — Probable function of ocelli ... ... ••• ••• 1'^^ 



CHAPTER VIII. 



On problematical organs of sense — Muciferous canals of fish — 

 Deep-sea fish— Light-organs — Living lamps — Problematical 

 organs in lower animals — Medusae- Insects — Crustacea — 

 Difficulty of problem— Size of ultimate atoms— The range 

 of vision and of hearing — Unknown senses — The unknown 

 world ... ... ... ... ... ... 182 



CHAPTER IX. 



On bees and colors— Experiments with colored papers — Dr. 

 Miiller's objections— Reply to objections — Preferences of 

 bees — The colors of flowers ... ... ... ... 194 



CHAPTER X. 



On the limits of vision of animals — Ants and colors— The 

 ultra-violet rays— The limits of vision in ants— Supposed 

 perception of light by the general surface of the skin — 

 Experiments with hoodwinked ants— Confirmation of my 

 experiments on ants — Experiments with Daphnias — Daph- 

 nias and colors— Preference for yellowish green — Experi- 

 ments — Limits of vision of Daphnias — Perception of 

 ultra-violet rays— Objections of M.Merejkowski— Suggestion 

 that Daphnias perceive brightness, but not color — Further 

 experiments — Evidence that Daphnias perceive differences 

 of color ... ... ... ... ... ••• 202 



CHAPTER XL 



On recognition among ants — Experiments with intoxicated ants 

 — Evidence against recognition by means of a sign or pass- 

 word — Experiments with ants removed from the nest as 



