52 



THE SCOLYTID BEETLES. 



DIGESTIVE SYSTEM. 



The general character of the digestive system is shown in figure 

 35, and no further explanation is necessary in this connection than 

 that given in the legend under figures 35 and 36. In figure 36 some 

 of the details of the internal anatomy of the fore mtestine are shown, 



and especially the structures and 

 elements of the proventriculus and 

 hypopharynx. 



^(Esophagus 



i^ii 'Aa ~" 'Proventriculus 



VentriculuS 



SECONDARY SEXUAL CHARAC- 

 TERS. 



While there are certain clearly 

 defined secondary sexual characters 

 in these beetles, they have not been 

 recognized by other writers, and 

 they were not found by the present 

 writer until after much detailed 

 study of the genus. When they 

 were determined it was surprising 

 how such prominent characters 

 could have been overlooked. Thus 

 we have another example of how 

 thoroughly familiar one must be 

 with a given group in order to rec- 

 ognize and properly interpret the 

 significance of characters in struc- 

 ture, sculpture, vestiture, etc. In 

 the first subdivision of the genus 

 the females are distinguished by a 

 transverse ridge across the anterior 

 area of the pronotum, while the 

 males are distinguished by the ab- 

 sence of this ridge and by more 

 prominent frontal tubercles which 

 are separated by a deeper frontal 

 groove. 



In the second subdivision the 

 females are distinguished by the 

 smoother and more shining elytral 

 declivity. In the third subdivision 

 the females have the elytral declivity distinctly more rugose, while 

 that of the males is smooth and shining. Thus we have a reversal 

 of the secondary sexual characters within the same genus, which is 

 an unusual occurrence. 



^ ^'Cohn 



■ctum 



Fig. 35. — Dendroctonus valens: Digestive organs 

 of adult. A, Fore intestine; B, mid intestine; 

 C, hind intestine; a, anterior section of mid in- 

 testine; b, median section of mid intestine; c, 

 posterior section of mid intestine; d, ccecal 

 glands; e, ileum or small intestine; /, base of 4 

 malpighian tubes; g, base of2malpighian tubes. 

 (Original.) 



