^"''u)i6 '] I.i'^wis, Some Considerci/ioiis on 5/^'/// /// liiyds. 22^ 



ill birds we can only theorize, while there may he jMesenl eon- 

 (lilions outside onr comprehension ol tlu' |)o\vei"s ol the eye. 

 There is still nuuli to be K'arned conct'iiiiiif^f aceommodation, 

 monoeular \isioii. eolonr \'isioiu and the [niietioii of the pecten. 



Explanation of Plates. 



Plate XXXIIl. 



Fig. 1 .—Globes of the eye of Horned Owh Skull dissected away to 

 show comparative size of eyes to tlie In-aiii. Cornea removed 

 from right eye. Specimen shows the tubular eye of near- 

 sighted night birds, the eyes capable of forward vision, both 

 seeing practically the same field of vision . 



Fig. 2.— Eye of Emu dissected to show anterior and posterior chamber 

 of globe, showing well-developed pecten, almost spherical eye, 

 flattened lens. Type of eye normally focussed for distance. 



Plate XXXIV. 

 Delicate Owl, showing eyes capable of forward double vision. 



Plate XXXV. 



Nankeen Kestrel, showing eyes capable of seeing a single object with 



both eyes, though total visual fields varying greatly. 



Plate XXXVI. 

 Crested Pigeon. \'ision totally monocular, both visual hclds differing, 

 either field capable of suppression in concentration of the 

 other eye on a single object. 



Illustration in Text. 

 Plain Wanderer. Type of total monocular vision. Both visual 

 fields distinct. 



Eggs of Reptiles and Birds Compared, with Some 

 Unusual Examples of the Latter. 



By Dr. K. W. Shufeldt, C.M.Z.S., WashinCxTon, D.C. 



Inasmuch as reptiHan characters of one kind or another are 

 constantly being found to exist in birds — a few here and more 

 there — it is not at all surprising that, when we come to study 

 extensive series of birds' eggs, laid by species representing avi- 

 faunae of widely-separated regions of the world, we meet with 

 those of some species which, in one way or another, exhibit 

 reptilian characters. Such discoveries furnish additional evidence 

 establishing the fact that these two groups in nature arose from 

 some common, pristine stock, while their differentiation at present 

 is very thorough and complete. This last is becoming more and 

 more so as certain species are entirely exterminated through 

 man's agency — that is, many birds, exhibiting in their economies 

 an unusual number of characters indicating the reptilian origin 



