140 



ENTOMOLOGY 



of a kind of premature development (known as prothetaly) in which 

 characters normally present in the pupal state are present abnormally in 

 the larva. The latter interpretation is supported by the fact that in 

 Mr. Powell's specimen, in addition to the larval ocelli, the compound 



eyes of the adult are partially 

 developed, and there are more 

 antennal segments than in the 

 normal larva. 



Ametabola. The most gen- 

 eralized insects, Thysanura and 

 Collembola, develop to sexual 

 maturity without a metamor- 



FiG. 2ii. Three eggs of the cabbage butter- phosis; the form at hatching is 

 fly, Pieris rapes. Greatly magnified, but all ' . , . ,, . , 



drawn to same scale. 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- 

 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. 



Stadium and Instar. During the growth 

 of every insect, the skin is shed periodically, 

 and with each molt, or ecdysis, the appearance 

 of the insect changes more or less. The inter- 

 vals between the molts are termed stages, or 

 stadia. To designate the insect at any particu- 

 lar stage, the term Instar was proposed and is 

 much used; thus the insect at hatching is the 

 first instar, after the first molt the second instar, 

 and so on. 



Eggs. The eggs of insects are exceedingly 

 diverse in form. Commonly they are more or 

 less spherical, oval, or elongate, but there are 

 innumerable special forms, some of which are 



f . . r, ,T r ,1 . , r FIG. 212. Chrysopa, laying 



quite fantastic. Something of the variety of eggs . Slightly enlarged. 

 form is shown in Fig. aio. As regards size, 



most insect eggs can be distinguished by the naked eye; many of 

 them tax the vision, however, for example, the elliptical eggs of 

 Dasyneura leguminicola, which are but .300 mm. in length and .075 



