72 INTERNAL STRUCTURE. 



sures run down, forming a collar around the oesophagus to 

 the ventral nerve-chain. This consists of commissural 

 fibres, with the following ganglionic enlargements: A sab- 

 cesophageal ganglion, (Fig. 40, uG), situated in the head, 

 and sending nerves to the mouth-parts ; one ganglion for 

 each thoracic segment ; four abdominal ganglia, one in the 

 second, one in the fourth, one in the sixth, and one in the 

 seventh segment. On each side of the nerve-chain, in the 

 second and third thoracic and the first to seventh ab- 

 dominal segments, are found apodewata, or projections 

 from the sterna which support the nerve-chain. 



METAMORPHOSES. 



Like all other insects, the orthoptera, in growing, have 

 to throw off their old skins and replace them with new and 

 more commodious ones. In some orders the forms assumed 

 after the various molts differ greatly ; in butterflies, for in- 

 stance, the caterpillars do not in the least resemble their 

 parents, and the chrjsalids or pup^e neither look like butter- 

 flies nor like caterpillars. All members of the order of or- 

 thoptera pass through an incomplete metamorphosis, i. e. 

 the young insects differ but slightlv from the adult ones. In 

 the locusts the most striking differences are the absence of 

 wings and the narrov^er and flattened prothorax, which is 

 much more roof-like than in the adult. The abdomen is 

 also quite different and more roof-shaped. The winged form 

 is gradually assumed through a series of molts, varying 

 from three or four to six. Species in which the wings are 

 either entirely wanting, or that possess only rudimentary 

 ones, generally pass through fewer molts than those having 

 large w^ings when adult. The wings first appear as small 

 wing-pads, which gradually become larger and larger, as 

 maj^ be seen in the illustration, (Fig. 42). As soon as the 

 wings appear, the insect ceases to grow. There is no state 

 of quiescence or rest in orthopterous insects as with in- 

 sects that undergo a complete metamorphosis, and the 



