STUDIES OF VARIATION IN INSECTS 



317 



lescing with its left or right-hand neighbor. In a lot of 149 

 individuals collected under stones on a hillside near San Jose, 

 on April 4, 1903, a number of classes were established on the 

 basis of the character of the two lines, one on each elytron, lying 

 on either side of the median groove which indicates the suture 

 of fusion of the inner margins of the two elytra. These lines 

 are referred to as a 1 and a* and either may have a short branch 

 called # lb or # rb , or simply a* when referred to for both sides 



(fig- 81.) 



The beetles are insects of complete metamorphosis and their 

 imaginal structural characters appear at once, on the issuance 



m 



\ 



FIG. 81. The predaceous ground beetle, Pterostichns sp., and diagram of 

 elytron (much enlarged), showing striae. 



of the imago (after the brief necessary expanding and drying of 

 wings, appendages and body-wall) in definite and fixed condi- 

 tion. Variations in these elytral striae are to be looked on as 

 strictly congenital in character. 



The classes and their frequencies based on the variations in 

 the character of lines a 1 and a* in the lot of 149 individuals are 

 as follows : 



Class A : 102 individuals have lines a 1 and a* separate on 

 both elytra. 



Class B : 4 individuals have line a b continued to line a on 

 both elytra. 



Proc. Wash. Acad. Sci., Dec., 1904. 



