CONTENTS. IX 



of Crustacea — Structure of eye — My sis — Corycsous— Copilia 

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

 l^hausia— Mode of vision by compound eyes— Miiller'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 ... ... ... ... 146 



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 



