DIMORPHISM IN BLISSUS LEUCOPTERUS. 



J. F. CAREER. 



Two forms of the chinch bug are recognized by entomologists 

 the one having wings fully developed, the other having wings 

 more or less abortive. Between the two extremes of fully winged 

 and almost wingless all gradations exist. Where the short- 

 winged form occurs it is usually intermixed with long-winged 

 individuals. Such a mixture appears at certain times in abun- 

 dance in the timothy meadows of northeastern Ohio. It was 

 from Trumbull, Portage, Mahoning and Stark counties of this 

 state that Professor F. M. Webster furnished the principal portion 

 of the material for the present study. 



The study was undertaken with the direction of Professor C. 

 B. Davenport to determine by quantitative methods the biological 

 significance of the dimorphism. 



METHOD. 



The insects examined represented several random collections 

 from different points. For study they were taken from the vari- 

 ous bottles with no attempt at selection so those studied are 

 presumed to present fairly the conditions in the whole group. 



Where practicable, the wings were carefully removed from the 

 body and mounted in a series on glass slides. By means of a 

 dissecting microscope of low power and a camera lucida the 

 image of the wing was projected upon a magnified scale and the 

 length thus read to tenths of a millimeter. With museum 

 material it was necessary to measure the wings in situ and this 

 was accomplished by the use of a metal scale divided to fifths of 

 a millimeter placed against the wing under a lens. 



THE FREQUENCY POLYGONS. 



The size of a class was fixed at one fifth of a millimeter and 

 this gave a range of ten classes. The polygon is bimodal, one 

 mode being at 1.5 mm. and the other at 2.7 mm. The extremes 

 of the range include from i mm. to 2.99 mm. 



