Entomology : with special reference to its biological and economic aspects . MOLOGY segments of the germ band. Fig. 196. 200, ;/) which have been derived by direct prohferation fromthose of the germ band, and are therefore ectodermal in primitive double nerve cord becomes constricted at inter-vals into segments, or ncuronicrcs, which correspond to the Each neuromere consists of apair of primitive ganglia, and theseare connected together by pairednerve cords, which later may ormay not unite into single cords;moreover, some of the gangliafinally unite to form compoundganglia, such as
Entomology : with special reference to its biological and economic aspects . MOLOGY segments of the germ band. Fig. 196. 200, ;/) which have been derived by direct prohferation fromthose of the germ band, and are therefore ectodermal in primitive double nerve cord becomes constricted at inter-vals into segments, or ncuronicrcs, which correspond to the Each neuromere consists of apair of primitive ganglia, and theseare connected together by pairednerve cords, which later may ormay not unite into single cords;moreover, some of the gangliafinally unite to form compoundganglia, such as the brain and thesuboesophageal ganglion. In frontof the oesophagus (Fig. 55) arethree neuromeres: (i) protoccrc-bnnii, which is to bear the com-pound eyes; (2) dciitocercbnim, orantennal neuromere; (3) tntoccrc-bniui, which belongs to the seg-ment which bears the rudimentaryintercalary appendages spoken ofabove. Behind the oesophagus are,at most, four neuromeres, namelyand in order, iiiaiidibitlar, siipcr-liiigitol (found only in Collembolaas yet), maxillary and Embryo of CEcanthus, ventralaspect. a, antenna; a^-a^, ab-dominal appendages; e, end ofabdomen; /, labrum; //, leftfundament of labium; Ip, labialpalpus; P~P, thoracic legs; m,mandible; mp, maxillary palpus;mx, maxilla; p, procephalic lobe;pr, proctodaeum.—After Ayers. Then follow the three thoracic gan- glia and ten (usually) abdominalganglia. The first three neuro-meres always unite together toform the brain, and the next four(always three; but four in Col-lembola and perhaps other insects), to form the suboeso-phageal ganglion. Compound ganglia are frequently formedalso in the thorax and abdomen by the union of primitiveganglia. DEVELOPMENT 153 Tracheae.—The trachere begin as paired invaginations ofthe ectoderm (Fig. 201, f) ; these simple pockets elongate and Fig. 197.
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectentomology, bookyear1
