Mar., 1908.] Brues : Mutation Among Insects. 51 



species, several subapterous ones, and others entirely destitute of 

 wings. In fact it seems probable that some of the normally volant 

 species are occasionally only partly winged in both sexes. So far as 

 primary function is concerned, a condition of slight reduction in the 

 size of the wings is equivalent to their complete absence, since once 

 below the standard required for flight, they are entirely useless, and 

 hence cannot be of selective value, unless in respect to some secondary 

 function which is extremely rare. Among related families other 

 genera exhibit closely similar conditions, e. g., Ca/ote/eia, Gryon, 

 Hoplogryon of the Scelionidae ; Loxotropa of the Diapriidae, etc. 



The occurrence of brachypterous forms of winged species has 

 often been noted in widely separated groups of insects, but is usually 

 the expression of seasonal or sexual dimorphism. At least in the 

 Hymenoptera above referred to, the regular occurrence of these wing- 

 less forms without intermediate stages points in the same direction as 

 the cases of wingless beetles, toward the existence of mutation as a 

 factor, and a very prevalent one. It is interesting to note in this 

 connection that Darwin himself mentions certain species of beetles 

 that are normally winged, but which occasionally have vestigial wings. 



So-called sports or mutations are not so rare in the wings of 

 Hymenoptera which are completely winged, and there have recently 

 come under my observation several very interesting cases. The first 

 series of three abnormal specimens belong to the same species, Myzine 

 sex-cincta Fabr., a member of the aculeate family Scoliidae. The 

 genus Myzine is notable for its strong sexual dimorphism that extends 

 even to the venation of the wings which is very different in the sexes. 

 This is a most remarkable character which is repeated in only a very 

 few instances throughout the entire order with the exception of a few 

 related Scoliid genera which are strongly dimorphic in this respect. 

 In other groups the dimorphism usually affects only a single cell such 

 as the radial. 



All three abnormalities are in male specimens (selected from a 

 series of not more than fifty) in which sex the venation also shows in 

 any considerable series of specimens a strong tendency toward con- 

 tinuous variation in the length of certain veins, insertion of recurrent 

 nervures, etc. 



That this variation, both continuous and discontinuous is cor- 

 related with the sexual dimorphism and the great variability of the 

 related genera seems very probable, and shows that the group as a 



