STUDIES OF VARIATION IN INSECTS 



247 



that this character of number of hooks is in a stable condition, . 

 tending neither manifestly to increase or decrease. 



Fig. 36. Frequency polygon of the variation in number of costal hooks of 

 the right hind wings of 181 male black ants; mean S.7 ; index of variability 

 1.086; coefficient of variation 1.25. 



Referring to the correlation between right and left wing in 

 this character of number of costal hooks 90 individuals (out of 

 189) have each wing with 8 or 9 (the double mode) while 99 

 have at least one wing departing from the mode. Of these 99 

 individuals with one or both wings varying, 21 have both wings 

 with less than 8 hooks, 9 have both wings with more than 9 

 hooks, while 3 have one wing with less than 8 and the other 

 wing with more than 9 hooks. Thus there is an obvious right 

 and left correlation, i. e., bilateral symmetry, in the variations. 



In going over the hind wings to count hooks, it was apparent 

 to the eye that there existed a variation in the degree of coales- 

 cence of the radial and medial veins at a certain point of touch- 

 ing (see fig. 34). The wings can be readily and fairly divided 

 into three classes based on differences in degree of this coales- 



