232 



KELLOGG AND BELL 



of these hooks " handles " for its work, if it ever is to take into 

 account variations in small but distinct characters which are in 

 immediate relation to the external environment of the organism. 



We have determined the variation in the number of costal 

 hooks in the hind wings of 300 drones from a laboratory hive 

 (Italians), the same lot whose wings have been studied for vari- 

 ation in character of venation and in linear dimensions of vein- 

 parts (see pp. 214 and 223). 



The variation in 279 left hind wings (21 of the 300 individ- 

 uals had torn wings) is graphically shown by the following fre- 

 quency polygon : 



Fig. 22. Frequency polygon of the variation in number of costal hooks of 

 left hind wings of 279 drone honey bees taken from laboratory hive at one time ; 

 mean 23.36; index of variability 1.695; coefficient of variation 7. 25. 



The range in number of hooks is from 19 to 27 ; the mean is 

 23.36, the mode 23, the standard deviation 1.695, and the coef- 

 ficient of variation 7.25. Eight3'-two individuals (29I per cent.) 

 have a smaller number of hooks than the mode (and than the 

 mean) while one hundred and thirty-one (47 per cent.) have a 

 larger number. The number having the mode is sixty-six (23I 

 per cent). 



