108 BULLETIN 195, UNITED STATES NATIONAL MUSEUM 



an experience. John Muir (1894) saw one "cheerily singing within 

 reach of the flying chips" from a man that was chopping wood on 

 a river bank. "On the lower reaches of the rivers where mills are 

 built, they sing on through the din of the machinery, and all the noisy 

 confusion of dogs, cattle, and workmen." This does not mean that 

 the ouzel does not need protection, or that it can adapt itself to civili- 

 zation, for it is slowly disappearing from some of its former haunts 

 where its living conditions have been altered, and it may eventually 

 find a suitable habitat only in some national park or other protected 

 reservation, 



A striking habit of the water ouzel, which has caused considerable 

 discussion and difference of opinion, is the frequent winking of either 

 the nictitating membrane or the upper eyelid, which has a narrow 

 border of short, white feathers. Some contend that the wink is pro- 

 duced by the membrane, and some say that it is the eyelid that pro- 

 duces it. As a matter of fact, I believe that it may be produced by 

 either feature of the bird's anatomy at different times. Grinnell and 

 Storer (1924) say: "The nictitating membrane or 'third eyelid' is 

 whitish in the Dipper, and, when drawn backward across the eye, as 

 it is frequently when the bird is above the water, can be seen at a 

 considerable distance. This membrane probably is drawn over the 

 eyeball when the bird is working beneath the surface of the water." 

 I cannot agree that this last assumption is correct; this membrane 

 is translucent, but not transparent, and would probably impede rather 

 than help the bird's vision where it would need it most; even the 

 unaided human eye can see under water; and I doubt if the trained 

 eye of the dipper needs this protection. 



Mr. Ehinger (1930), "being at very close range noted particularly 

 the winking of the white-edged eyelids and the flash of the third lid 

 or nictitating membrane. When the bird was facing me the winking 

 seemed simultaneous with both eyes; when but one eye was turned 

 toward me the nictitating membrane seemed to flash out from different 

 portions of the eye and at times as though it came from the outer 

 canthus." 



Dr. Cordier (1927) collected considerable evidence on this subject, 

 to which the reader is referred, and made some thorough, close-up 

 observations, which seem to throw considerable light on the subject, 

 and from which I quote as follows : 



My observations leading to these conclusions were made at a range of 4 feet 

 to 18 inches from the bird, extending over several hours each day for several 

 days. The winking in this bird was performed by the action of the nictitating 

 membrane and not by the upper eyelid. The upper eyelid has a well defined 

 white margin. From beneath this, the membrane was flashed in a downward 

 direction in rather an oval shape, extending to the lower border of the cornea. 

 The moving pictures show this membrane very distinctly. The movement is 

 seen to come from above downward, nearhi the horizontal tmdth of the upper eye- 



