PRELIMINARY CLASSIFICATION OF SCOLYTOIDEA, 215 



PROGRESSIVE MODIFICATIONS. 



The discontinuous yet more or less progressive cliange or variation 

 in the modification of morphological and physiological elements 

 along definite lines within the minor to major groups is very evident 

 in every group. The more this subject is studied the more we are 

 convinced that there are certain important facts involved in this 

 principle that have not been satisfactorily explained by any theory 

 of the processes of evolution. The recognition and application in 

 taxonomy of those unexplained features does not, however, neces- 

 sarily require the acceptance or rejection of any theory of ortho- 

 genesis or phylogenesis. It is only necessary to correlate them with 

 other more easily explained elements of distinction or to utihze them 

 as guides to the position a species or group should occupy in a given 

 series. 



Examples of Progressive Modification. 



The examples of progressive modification m morphological char- 

 acters and physiological characteristics which have been noted by 

 the writer in the scolytoid beetles may be summarized as follows: 



Morphological characters. 



Body small to large. 



Body slender to stout. 



Body with scales to hairs, to glabrous. 



Head concealed to exposed. 



Head short and broad to narrow and sub rostrate. 



Head with front convex, glabrous, to concave and pubescent or fringed. 



Head with eyes oblong, elliptical and not emarginate, to short, oval, and deeply 

 emarginate or divided. 



Antennal joints of funicle increasing in number to the limit of seven. 



Antennal joints of club decreasing in number through fusion or disappearance of 

 sutures. 



Prothorax long and narrow to short and broad. 



Prothorax with sides not margined to margined, or not emarginate to emarginate. 



Prothoracic pleurum convex to flat and concave. 



Tarsi with third joint simple to emarginate and bilobed. 



Tarsi with first joint short to long. 



Elytral declivity convex and smooth to rugose and armed; retuse to concave, with 

 the margin unarmed to strongly armed. 



Sexes of unequal size and the males rare to equal size and the males common. 



Secondary sexual characters obscure to prominent. 



Galleries. 



Simple cavities in decaying bark and wood, to complex designs and regular forms of 

 egg galleries and larval mines. 



Excavated in bark to excavated in wood, seeds, etc. 



Social habits. 



Unorganized polygamy to organized polygamy, to highly organized monogamy. 

 Independent larvae, procuring their own food, to dependent larvae, with the food 

 provided by the maternal parent. 



