128 



ENTOMOLOGY 



at hatching is retained essentially throughout life, there are no traces of 

 wings even in the embryo, and there is no change of habit. These two 

 orders form the group Ametabola. All other insects have a metamor- 



FIG. 207. Cicada tibicen. A, imago emerging from nymphal skin; B, the cast skin; C, 



imago. Natural size. 



phosis in the broad sense of the term, and are therefore spoken of as 

 Metabola. In this we follow Packard, rather than Brauer, who uses a 

 somewhat different set of terms to express the same ideas. 



FIG. 208. Eggs of various insects. A, butterfly, Polygonia inter rogationis; B, house fly, 

 Musca domestica; C, chalcid, Bruchophagus funebris; D, butterfly, Papilio troilus; E, midge, 

 Dasyneura trifolii; F, hemipteron, Triphleps insidiosus; G, hemipteron, Podisus spinosus; 

 H, fly, Drosophila ampelophUa. Greatly magnified. 



Stadium and Instar. During the growth of every insect, the skin 

 is shed periodically, and with each moult, or ecdysis, the appearance of 

 the insect changes more or less. The intervals between the moults are 

 termed stages, or stadia. To designate the insect at any particular stage, 

 the term instar has been proposed and is growing in favor; thus the 



