PREFACE 



The stmctural patterns of vertebrate eyes have been undergoing 

 intelligent scrutiny for about a century and a half. In that time, and 

 more and more rapidly toward the present, men have been learning 

 much about the functional meanings of those patterns, and their roles 

 in the lives of the animals which have produced them. It has seemed 

 to me that it is time an attempt was made to interpret comparative 

 ocular biology as a whole to those who want to know what the eye is 

 all about, but are repelled by the pedantic terminology of anatomy 

 texts, the mathematics of physiological optics, the scatteredness of the 

 ecological literature, and the German language. In this book, I have 

 made such an attempt. 



I have chosen the term 'adaptive radiation' for the subtitle of this 

 work deliberately. It was coined by Henry Fairfield Osborn to describe 

 the manner in which animal groups have become diversified in pouring 

 themselves into a number of environmental molds which were made 

 available to them more or less simultaneously. It is a little unusual to 

 speak of the adaptive radiation of an organ; but I can think of no 

 better way to express what the vertebrate eye has done in modifying its 

 pattern to fit itself for the many different kinds of performance de- 

 manded of it by its adaptively-radiated owners. 



The investigation of anatomy for its own sake is pretty well defunct. 

 The study of structures in relation to their employment by the animal 

 has hardly begun. When I started writing this book, I had never heard 

 of the late Hans Boker; but, in discussing the eyes of vertebrates in 

 terms of adaptation to environment, I believe I have followed the prin- 

 ciples of his 'comparative biological anatomy', which have so revivified 

 the study of anatomy in recent years. 



If the comparative ophthalmologists of the world should ever hold 

 a convention, the first resolution they would pass would say: "Every- 

 thing in the vertebrate eye means something." Except for the brain, 

 there is no other organ in the body of which that can be said. It does 

 not matter in the least whether a liver has three lobes or four, or 

 whether the tip of the heart points north or south, or whether a hand 

 has five fingers or six, or whether a kidney is long and narrow or short 

 and wide. But if we should make comparable changes in the makeup of 



