CHAPTER XVII 

 THE VISION OF INVERTEBRATES 



I am introducing this chapter on the function of the ej^es of Invertebrates 



with the photograph of karl von frisch (1886 ) (Fig. 728), who has devoted 



his long and fruitful life to the fascinating study of animal behaviour — and still 

 continues to do so. Born in Vienna, he studied in Munich and successively 

 became Professor and Director of the Zoological Institutes at the Universities 

 of Rostok (1921), Breslau (1923), Munich (1925), Graz (1946), and again Munich 

 (1950) where, as this book is being written, he is still pursuing his close and 

 intimate study of the habits of insects. Taken as a whole, his life as a biologist, 

 spent observing the behaviour of his experimental friends in the water and in 

 the covmtryside, must have been a delightful one ; he obviously enjoyed it and 

 no one can read his published works without realizing that fact can indeed be 

 more exciting and of more interest than fiction. The greater part of the first years 

 of his stvidies was devoted to the vision, and particularly the colour vision, of 

 fishes, a subject in which, as we shall see in the following chapter, he became a 

 great avithority, opposing the views of Carl von Hess (Fig. 735) and eventually 

 winning the battle. The latter part of his life has been largely spent observing the 

 habits of bees. Much of the fruits of this we have already studied in the chapter 

 on the influence of light on movement .^ There are few romances in science more 

 pleasant than the convincing and far-reaching results he has obtained in the 

 study of the extraordinarily complex behaviour of these insects in the meadows 

 of Central Europe ; and there are few pieces of biological work carried through 

 with greater perseverance, with greater thoroughness and to greater purpose. 



METHODS OF INVESTIGATION 



The scientific estimation of tlie visual capacity of animals is 

 notoriously difficult. It is a difficult problem even in man for sensations 

 are individualistic and subjective and the language of introspection 

 is usually unsafe ; in the lower animals the difficulties become in- 

 finitely greater for the only criterion whereon we can pass judgment is 

 the observation of their reactions to various stimuli ; we have no 

 knowledge of how far their exj^eriences coincide with our own, and no 

 right to equate the two.- 



From the scientific point of view the observation of animal 

 behaviour in ordinary uncontrolled circumstances can provide much 

 useful information regarding their sensory experiences, but from such 

 evidence our conclusions can only be drawn with reserve. This 

 approach is full of j^itfalls even in human subjects. A red-green 

 colour-blind person will say that he can appreciate red and green and 

 usually behaves as if he does so ; and we have little idea of what 



p. 70. 2 p. 108. 



