212 THE SCOLYTID BEETLES, 



and the wide range in their variation, together with tlie disturbing 

 factors, or reversals, and parallel modifications, are enough to over- 

 whelm, confuse, and discourage anyone who attempts to study and 

 utilize them in a comprehensive classification. It is plain, however, 

 that it is only through such a comprehensive treatment that we can 

 hope to approach the ideal natural classification. 



MORPHOLOGICAL CHARACTERS. 



In a review of the morphological characters it is found that the 

 tarsus and tibia are of special value in the classification of the super- 

 family; the head, pronotum, elytra, and third joint of the tarsus for 

 the family; the head, tarsi, pronotum, elytra, anterior coxse, abdomi- 

 nal sternite, and pygidium for the subfamily; the antennae, eyes, 

 pronotum, elytra, tarsi, tibiae, body, abdominal sternites, anterior 

 coxse, and mouthparts for the genus, and for the species there is such 

 a wide range of characters of varying, and sometimes reverse, value 

 in different genera that they can not be specified except for limited 

 groups. However, the size, form, color, vestiture, and sculpture 

 of the body, the front of the head, elytral declivity, etc., are in gen- 

 eral among the most important bearers of specific characters. 



In the digestive system the masticatory plates of the proventric- 

 ulus appear to be of special taxonomic value when applied to sub- 

 famihes, genera, and species. 



In the reproductive organs of the male there is a very wide range 

 of variation in the primary and secondary elements of the posterior 

 or chitinized section, but with a few exceptions their taxonomic 

 value appears to be restricted to major and minor divisions of the 

 genus and especially to the separation of the species. In the anterior 

 section of the organs the length of the ductus ejaculatorius and the 

 form of the testes, seminal vesicles, vas deferens, and mucus glands 

 appear to represent the principal taxonomic elements, and they are 

 of varying value as applied to major and minor groups. 



The female reproductive organs, like the proventriculus, appear to 

 possess a number of taxonomic characters of family, subfamily, and 

 generic value, such as the presence or absence of the cement glands 

 and their varying characters and tlie presence and character of the 

 spermatheca with its seminal duct. 



In the secondary sexual characters we find a few which are peculiar 

 to a genus or to groups of allied genera, but m general their principal 

 value appears to be in distinguishing the species. 



In the pupae it is found that the head and the tergal, lateral, pleural, 

 caudal, and femoral spmes appear to be the most important taxo- 

 nomic elements. 



In the larvae there is a wide range of variation in the form of the 

 body and in some of the primary elements of the head and posterior 



