STUDIES OF VARIATION IN INSECTS 245 



plete metamorphosis, the adults (imagines) issuing from pro- 

 tected pupae, with all parts in definitive and unchangeable con- 

 dition (after the brief expanding and drying of wings, legs, etc., 

 immediately on appearance). Variations in the adult are to be 

 looked on as congenital. 



A lot of 200 male winged ants of one species (undetermined), 

 collected at one time from one place, has been studied for vari- 

 ation in the number of hooks on the costal margin of the hind 

 wings, for variation in the dimensions of the fore wings and 

 restricted parts of the veins, and for variation in the character 

 of the venation in the hind wings. These ants had issued for 

 their mating and distributing flight and had fallen exhausted on 

 the surface of the water in a watering trough. They were 

 probably members of a single community, or, at most, of two 

 or three neighboring nests. 



FIG. 34. Fore and hind wings of male black ant, showing normal venation, 

 lettered parts of veins referred to in data of measurements, hooks on costal 

 margin of hind wing, and three degrees of fusion of certain veins referred to in 

 text. 



The hind wings of ants are provided with a series of small, 

 strong curved spines or hooks along the costal margins of the 

 wings (fig. 34). When the wings are expanded these hooks 

 grasp a thickened vein in the hinder margin of the fore wings 

 and securely tie or hold the two wings of each side together, 

 thus making them vibrate perfectly synchronously, or indeed as 

 a single wing. The hooks are undoubtedly important structures 



