46 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- 
eual 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. 
Paramedian section of an embryo of the collembolan Anurida maritima, to show 
the primitive cephalic ganglia. 7, ocular neuromere; 2, antennal; 3, intercalary; 4, 
mandibular; 5, superlingual; 6, maxillary; 7, labial; 8, prothoracic; 9, mesothoracic; 
a, antenna; 7, labrum; /i, labium; 7, /?, , thoracic legs; m, mandible; mu, 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 propodeum, or median seg- 
ment. Each of the three thoracic segments bears a pair of 
