CLASSIFICATION OF AVES AND THE FUNDUS OCULI 



115 



form of an orange-red coloration) may be 

 present to indicate not so much recent as 

 former, i. e. atavistic, night habits long since 

 abandoned by the species. 



This almost universal occurrence of yellow 

 or orange-tinted fundi in Night Birds leads 

 one to speculate as to the cause of a different 

 coloration in species that, during historic 

 times at least, have used their eyes largely or 

 exclusively after dark. At least some of the 

 Ardeiformes furnish such examples. The fun- 

 dal coloring of Nycticorax nycticorax (Plate 

 XX) has no yellow in it; nor has the Boatbill 

 (Cancroma cochlearia), although both fundi 

 are evidently so closely allied that one might 

 well believe that they are both Herons. 

 Probably the Night Herons have adopted an 



exclusively nocturnal life at such a recent 

 geologic period that the evolutionary tissue 

 changes necessary to produce the yellow fun- 

 dus tints have not yet been brought about. 

 The same remark is applicable to the Bittern 

 (Plate XXI). 



So far as examined, the decidedly nocturnal 

 Caprimulgidae also have yellow or orange 

 fundi. The eyeground of the European 

 Nightjar (Plate XLIV) is a conspicuous and 

 typical example of the colored fundus of a 

 true Night-feeding bird. 



The arrangement of the centres of distinct 

 vision, the fundus tints and the pectinate 

 tissues of the larger Acciptriformes present a 

 decided ophthalmoscopic resemblance in all 

 the species so far examined by the writer. 



