40 ENTOMOLOGY 



behind the mouth eventually combine to form the subcesopha 

 geal ganglion. 



To summarize the head of an insect is composed of at least 

 six segments, namely, ocular, antennal, intercalary, mandibu- 

 lar, maxillary and labial ; and at most seven, since a superlin- 

 gual segment occurs between the mandibular and maxillary 

 segments in Collembola and probably Thysanura, though it 

 has not yet been discovered in the more specialized insects. 



FIG. 55. 





8 



Paramedian section of an embryo of the collembolan Anurida maritima, to show 

 the primitive cephalic ganglia. I, ocular neuromere; 2, antennal; 3, intercalary; 4, 

 mandibular; 5, superlingual; 6, maxillary; 7, labial; 8, prothoracic; 9, mesothoracic;. 

 a, antenna; /, labrum; li, labium; P-, l z , I 3 , thoracic legs; m, mandible; mx, maxilla. 

 After FOLSOM. 



Thorax. The thorax, or middle region, comprises the- 

 three segments next behind the head, which are termed, respec- 

 tively, pro-, meso- and metathorax. In aculeate Hymenop- 

 tera, however, the thoracic mass includes also the first abdom- 

 inal segment, then known as the propodewn, or median seg- 

 ment. Each of the three thoracic segments bears a pair of 



