Chapter II 

 SUMMARY OF CONCLUSIONS 



1. The examination of the eyes of Birds 

 is a study of the most advanced and most 

 varied apparatus for the highest expression 

 of vision known to any vertebrate class. 



2. The examination of the interior of the 

 avian eye through the pupil of animate species 

 (ophthalmoscopy) gives valuable information 

 regarding the function of sight in general and 

 of the eyesight of Birds in particular. 



3. The fundus oculi, or background of the 

 eye, is plainly seen in its normal relations 

 when viewed during the life of the species, 

 and in many respects this form of exploration 

 is superior to methods carried out on prepared 

 or preserved eyeballs. 



4. The parts and organs visible by the 

 ophthalmoscope in the eye of the Bird are in 

 particular (a) the concavity or general chorio- 

 retinal surface of the posterior half of the 

 eye; (b) the pecten; (c) the optic nerve en- 

 trance; (d) the areas of acute vision; (e) the 

 fundal bloodvessels; (J) opaque nerve fibres. 



5. The appearances of these organs and 

 tissues furnish entirely different, colored fun- 

 dus pictures, and it is frequently possible to 

 recognize a species by viewing its fundus 

 oculi. 



6. The fundus oculi of Birds exhibits a 

 great variety of areas of distinct vision, and 

 these correspond closely to the habits and 

 habitat of these animals — especially their 

 methods of obtaining food, of escape from 

 enemies, of migration, of reproduction, etc. 



7. In spite of recent advances in that di- 

 rection, attempts to reproduce the colored 

 (ophthalmoscopic) appearances of the fundus 

 by photography have so far failed. 



8. The macroscopic appearances of the 

 ocular fundus resulting from an examination 

 of preserved specimens have a value in this 

 research all their own; for certain forms of 

 examination it is inferior to ophthalmoscopy, 

 for others superior; but it gives no indication 

 of the color tones of the background so well 

 shown by the ophthalmoscope. 



9. As in ophthalmoscopy, attempts to re- 

 produce the details of the eyeground of pre- 

 served specimens have so far given unsatis- 

 factory results. 



10. The use of the microscope in examin- 

 ing the avian eye, and especially serial sec- 

 tions of the parts, is occasionally required 

 to settle anatomical questions that neither 

 ophthalmoscopy nor macroscopy can eluci- 

 date. 



11. Domestication or prolonged captivity 

 brings about abnormal changes in the eye- 



- ground of Birds, so that only healthy, wild 

 specimens should be utilized in this or a 

 similar research. 



12. As the colored pictures seen in the 

 fundi of healthy wild birds are invariable in 

 species these appearances may well furnish 

 data for a classification of Aves ranking in 

 importance with other taxonomic indications. 



13. Ophthalmoscopy throws light on the 

 origin of Birds, or at least on their relation 

 to that Sauropsidian ancestry which they 

 hold in common with Reptilia. 



14. In future no report upon a particular 

 avian species can be held complete that 

 ignores the visual apparatus, and especially 

 the appearances of the fundus oculi as shown 

 by the ophthalmoscope. 



[7] 



