NATURAL SELECTION 



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tightly gripping the female. There is nothing to show that 

 the specific differences in grasping organs are adaptive, and 

 it would even sometimes appear that the structures were 



Fig. 27. — Forelegs of some Male Crabronidae. 



A. Thyreopus cribrarius L. Left foreleg, coxa omitted. Femur abnormal ; 



tibia strongly, tarsi moderately, broadened. 



B. Crossocerus palmarius Schreb. Tibia and basitarsus strongly broadened. 



C. C. palmipes van de Lind. Basitarsus broadened. 



D. C. elongatulus van de Lind. Leg unmodified. 



developed beyond the needs of the species, as far as we can 

 gauge these by comparison with allied forms. 



(c) The vast majority of sexually dimorphic structures, 



though still of great value as specific characters, appear to 



