106 



Natural Selection 



Fig. 43. Heads of the principle types of antelopes in the Congo. The horns 

 of all function satisfactorily, indicating that there is no one perfect type for 

 these stuctures. (After Schouteden.) 



bling the series of short wing mutants discovered by Lavan in the 

 mosquitoes (Fig. 36). Also, an extra terminal segment is variously 

 sclerotized. In these A. vivipara females, however, the two char- 

 acters are not correlated. In populations over a wide part of the 

 range, a third of the females with the shortest wings have the most 

 extensively sclerotized abdomens and a third have the least 

 sclerotized; conversely, of the females with the most extensively 



