A PECULIAR MONSTROSITY IN A FROG. 317 



to maturity with so very material an impediment. It makes 

 one ask just how much of a variation from the normal is needed 

 to enable natural selection to perform its cruel w r ork? 



ZOOLOGICAL LABORATORY, 



UNIVERSITY OF WISCONSIN, 

 July 31, 1913. 



BIBLIOGRAPHY. 



Adami 



'10 Principles of Pathology. 2cl edition. Vol. I. Philadelphia, Lea and 



Febiger. 

 Schwalbe 



'07 Die Morphologic der Missbildungen des Menschen und der Tiere, u.s.w. 



II. Teil. Jena, Fischer. 

 Sutton, J. B. 



'92 Evolution and Disease. London, Walter Scott. 

 Tornier, G. 



'05 An Knoblauchkroten experimentell entstandene uberzahlige Hinterglied- 

 massen. Archiv f. Entwickl. Mechanik, 20, pp. 76-124. 



