152 ENTOMOLOGY 
200, 2) which have been derived by direct proliferation from 
those of the germ band, and are therefore ectodermal in origin. 
This primitive double nerve cord becomes constricted at inter- 
vals into segments, or meuromeres, which correspond to the 
segments of the germ band. Each neuromere consists of a 
Tie. 106. pair of primitive ganglia, and these 
/ ay are connected together by paired 
1 
1 
' 
nerve cords, which later may or 
may not unite into single cords; 
moreover, some of the ganglia 
finally unite to form compound 
ganglia, such as the brain and the 
subcesophageal ganglion. In front 
of the cesophagus (Fig. 55) are 
three neuromeres: (1) protocere- 
brum, which is to bear the com- 
pound eyes; (2) deutocerebrum, or 
antennal neuromere; (3) tritocere- 
brum, which belongs to the seg- 
ment which bears the rudimentary 
intercalary appendages spoken of 
above. Behind the cesophagus are, 
at most, tour neuromeres, namely 
and in order, mandibular, super- 
lingual (found only in Collembola 
; as yet), maxillary and labial. 
fee ie, ee Then follow the three thoracic gan- 
dominal appendages; e, end of glia and ten (usually) abdominal 
abdomen; 7, labrum; Ji, left . rE n~ j 
fundament of labium; /p, labial ganglia. he first three neuro- 
palpus; /-/8, thoracic legs; m, 
mandible; mp, maxillary palpus; 
mx, maxilla; p, procephalic lobe; form the brain, and the next four 
pr, proctodeum.—After Ayers. 
meres always unite together to 
(always three; but four in Col- 
lembola and perhaps other insects), to form the subceso- 
phageal ganglion. Compound ganglia are frequently formed 
also in the thorax and abdomen by the union of primitive 
ganglia. 
