180 THE SCOLYTID BEETLES. 



a basal lobe. The wiiter has given considerable attention to tlie study 

 of the wings of the Scolytoidea and other insects, but he has failed 

 to find any constant and readily recognizable characters in the 

 Scolytoidea which appear to be of sufficient taxonomic value to 

 justify giving them special attention. If there is any particular 

 Hne of progressive modification in the wings it is to be found in the 

 subfamilies and minor groups, in which the range appears to be from 

 a simple type, like that of Hypothenemus, Cryplialus, and Cryp- 

 turgus, with a narrow, simple base, long fringe, and simple venation, 

 toward a broader base, lobed or not, and with an increasing number 

 and complexity of veins. The writer reaUzes that the complex 

 type of venation is generally supposed to be more primitive than 

 the simple type with few or no veins, but he is by no means convinced 

 that this is the correct interpretation as applied to the wings of all 

 insects. The wings in different orders of insects may be, in spite of 

 the prevailing opinion, the result of independent origin from simple 

 types of primitive winglike processes, and their evolution may have 

 been influenced by two primary factors: (1) A dominant tendency 

 to perpetuate and promote lines of modification peculiar to and in 

 conformity with the dominant morphological characters peculiar to 

 the order, and (2) adjustment of this modification to the peculiar 

 mechanical needs of the varying related forms, with frequent examples 

 of parallel modifications in unrelated species. 



In Niisslin's table (1911, pp. 302-304) the wings without basal 

 lobes are found in widely separated genera, representing, according 

 to the present writer's classification, two families (Ipidse and Scolytidse) 

 and five subfamilies, while the wings with basal lobes are found in five 

 subfamilies of the Ipidse. It is evident that whenever the wings 

 are studied in their relation to other of the more important taxonomic 

 characters and characteristics of the species, the variations noted 

 by Ntisslin will be of considerable value in the definition of minor 

 groups of genera and species, but the difficulty of spreading the 

 wings and securing good balsam mounts will preclude their general 

 use. 



ABDOMINAL TERGITES. 



The general character of the abdominal tergites is shown in Part I, 

 figures 22, 23, and 24. While there is considerable variation in the 

 first to sixth tergites, inclusive, in the same individual and between 

 individuals of different species, the seventh and eighth are the ones 

 of special importance in the identification of the genus or sex. Ac- 

 cording to Niisslin (1911), who examined 16 genera, the eighth ter- 

 gite is not covered in either sex in 11 genera, and is exposed in the 

 male and covered in the female in 5 genera. The writer has found 



