Mar., 1908.] 



Brues : Mutation Among Insects. 



47 



One genus, Pasiinachus, is particularly noticeable on account of 

 its large species of peculiar form which 

 are almost completely apterous. In 

 nine North American species which I 

 have been able to examine, the size and 

 shape of the wings is remarkably con- 

 stant (see fig. 1). In this respect all 

 closely resemble Pasimachus punctu- 

 latus Hald., the wings of which are 

 figured in a previous paper. They are 

 from three to four and one half milli- 

 meters in length, or about one third 

 the length of the elytron, with a dis- 

 tinctly broader basal and suddenly 

 narrower apical portion. So far as my 

 observations go, they are narrowest 

 in subside atus Say and broadest in 

 strenuus Lee. ; costifer Lee. shows the 

 most marked distinction between the 

 narrower and broader parts. None 

 have any trace of a venation except for 

 a slight costal thickening basally. 

 Thus throughout this entire genus the 

 wings are extremely reduced in size, 

 yet peculiarly constant. 



This constancy of form in all the 

 species would seem to indicate that 

 the type of wing must have been ac- 

 quired before the more recent origin 

 of the present species from a common 

 stock, and that it has been perpetuated 

 without any change during the later 

 differentiation of these species, unless p 1Gi 1 Outlines of hind wings 



we are willing to grant the presence in nine species of Pasimachus. I. P. 

 of a determinate evolution which has marginatut Fabr. ; 2. P. tubsulcatm 

 brought all to the same form more or Sa ^ 3- P. elongatus Lee; 4 - P. 



... . dupluatus Sav ; 5. P. costifer Ice. ; 



less independently. , „ .,-13 „ D 



1 J 6. P. subhiTis Beauv. ; 7. P. 



The extensive genus Calosoma be- p ,. essm Fabr . 8> />. punctvlatus 



onging to the same family exhibits an Hald. ; 9. P. strenuus Lee. 



