PREFACE 



The structure of the vertebrate retina in relation to its 

 function is a subject about which much has been written. 

 It might seem redundant, therefore, to add to the voluminous 

 literature already extant. This is especially true in view of 

 the recent appearance of two excellent books on the subject. 

 The first of these, by S. L. Polyak, appeared in October 1941, 

 while my writing was in progress; the second by G. L. Walls, 

 which was published in August 1942, did not appear until 

 after my manuscript had gone to the publishers. Despite 

 the admirable and comprehensive accounts by these two 

 authors, as well as previous shorter accounts by other writers 

 (Cajal, 1894; Greeff, 1900; Garten, 1907; Franz, 1913; Aiey, 

 1928; Kolmer, 1936 and others), I have been urged by my 

 colleagues to finish my story, with the assurance that this 

 monograph would adequately fulfill its originally intended 

 purpose as a handbook for those interested in the visual 

 apparatus of vertebrates. 



It has been my plan to bring together in this volume cer- 

 tain essential structural and functional features of the retina, 

 particularly of the photoreceptors. It has not been my pur- 

 pose to enter into the minutiae of histological detail, for this 

 would befog my original point of view which has been to 

 present an account of the retinal photoreceptors in such a 

 form as to be of value to those who have a general interest 

 in the biology of the retina, rather than to the specialist. 

 It is hoped, however, that it may be of definite service also 

 to those more specifically concerned with problems of retinal 

 physiology. 



Since it has been my design to make this monograph 

 relatively brief and readable, many omissions have been 

 necessary, particularly with respect to the vast literature on 

 the subject under discussion. 



S. R. D. 

 New York City 



