° 1915 ] Johnson, .4 Four-winged Wild Duck. 4/9 



development, mesiad of the accessory element; and there is no 

 reason to believe that the distal and proximal parts of the super- 

 numerary wing are not the result of the same cause. Furthermore, 

 it seems improbable that complications in the embryonic membranes 

 should arise on the two sides simultaneously, of such nature as to 

 produce substantially identical results. Taking this anomaly as 

 a whole, the extent to which the entire wing is involved, the imper- 

 fect separation of the accessory upper arm bone, the absence of 

 other impressions and disturbances in adjacent soft parts which one 

 might expect as a result of such agencies, there seems to me no basis 

 for believing that embryonic membranes have here been implicated 

 directly or indirectly. What other extrinsic agencies acting merely 

 on the skeletal anlage of the wing alone, or upon the wing-bud as a 

 whole, might have produced the conditions found, are difficult 

 to imagine. The more probable view for this case, it appears to me, 

 is that it resulted from some inherent abnormality of the anlage of 

 the extremity, of germinal origin. 



BIBLIOGRAPHY. 



Banta, A. M., and Gortner, R. A. 



1915. Accessory appendages and other abnormalities produced in 

 amphibian larvae through the action of centrifugal force. 

 Joum. of Exper. Zool., vol. 18. 

 Barfurth, D. 



1895. Die experimentelle Regeneration uebershlissiger Gliedmassen- 

 theile (Polydactylie) bei den Amphibien. Arch, fur Entw.- 

 Mech.,Bd. 1. 

 Bateson, Wm. 



1894. Materials for the Study of Variation. Macmillan & Co., 

 New York. 

 Bonnet, M. 



1777. Memoire sur la reproduction des membres de la Salamandre 



aquatique. Paris. Memoire X. 

 1779. Observation sur la physique, etc. par Rozier. Memoire XIII. 

 Broom, Robt. 



1897. On the anatomy of a four-winged chick. Trans. Nat. Hist. 

 Soc, Glasgow, N. S. vol. 4, pt. 3- 



DlARD, 



1897. Canard a quatre pattes (monstre pygomele). Bull. Soc. Hist, 

 nat., Autun. No. 10, pt. 2. 

 Dwight, Thomas. 



1893. Fusion of hands. Anat. Anz. 



