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KELLOGG AND BELL 



in the flight apparatus. These hooks vary in number in the 

 individuals of this lot, the following frequency polygons show 

 ing the range and character of this variation ^ for both right and 

 left hind wings. (See figs. 35 and 36.) 



Fig. 35. Frequency polygon of the variation in number of costal hooks of 

 left hind wings of 188 male black ants (sp. undetermined); mean 8.5; index 

 of variabilitj' 1.048; coefficient of variation 1.23. 



The range in each wing is thus from 6 to 1 1 hooks, a single 

 5-hook right wing occurring, while the mode in one wing, the 

 right, is 8 and in the other 9. It will be noted that in the right 

 wing, 9, in the left wing, 8, are nearly equally represented with 

 the mode, so that the true condition existing in this species is 

 probably bi-modal with the two modes, 8 and 9, being succes- 

 sive instead of separated numbers. The frequenc}^ curve is, 

 considering the brevity of the series, a fairly symmetrical one, 

 and in a large series would probabh' nearly coincide with the 

 theoretical curve (determined by the law of error) indicating 



' Where hooks were broken off or jerked out of their insertion pits they were 

 counted as present ; they were present at the time of the appearance of the adult, 

 i.e., congenitally present. 



