THE 



AMERICAN NATURALIST 



Vol. LIV. July-August\ 1920 No. 633 



INHEKITANCE OF CALLOSITIES IX THE 

 OSTEICH 



DR. J. E. DUERDEN 



Officer-in-Charge, Ostrich Investigations, Grootfontein 

 School of Agriculture. Middelburg, South Africa 1 



"The problem of the method of evolution is one which 

 the biologist finds it impossible to lea re alone, although 

 the longer he works at it, the farther its solution fades 

 into the distance. The central point in the problem is the 

 a ppe<t ranee, nature, and origin of the heritable varieties 

 that arise in organisms."— H. S. Jennings. 2 



The ostrich has a shield-like -termini devoid of a keel, 

 a character it shares with the rest of the Katitae. The 

 middle forms a broad, rounded ] >n» jt-et i< m. while the cov- 

 ering skin is greatly thickened, devoid of feathers, and 

 constitutes a large, dense callosity on which the bird rests 

 when crouching. Moreover, the ostrich is unique among 

 birds in having a symphysis pubis, which forms a ventral 

 projection behind corresponding with the one in front, 

 only smaller, the skin over it likewise showing a strong 

 callosity (Fig. 1). The result is that when the bird 

 crouches the two median projections come into direct 

 contact with the ground and the thickened pads support 

 the greater part of the weight of the body, about 250 lbs., 

 in front and behind, while it is steadied laterally by rest- 

 ing upon the upper surface of the nearly horizontal meta- 



