332 ZOOLOGY 



libera, that is, its appendages are free, and not hidden under a 

 covering, as is the case with the Lepidoptera. The pupal stage 

 lasts till the following spring, and in the interval the individual 

 has undergone great changes ; its nervous system, with a gan- 

 glion in each segment, has become concentrated, its wings have 

 developed, and its appendages have assumed their adult form. 

 The perfect insect or imago emerges from the pupa some little 

 time before it appears on the surface, but during the month of 

 May in its fourth year the mature cockchafer makes its way 

 above ground, and is found hanging underneath the leaves of 

 the trees which serve it as food. 



The life-history of Melolontha affords a good e.x;ample of a 

 complete metamorphosis, with its larval, pupal, and imaginal 

 stages. The egg gives rise to a larva which has little or no 

 resemblance to the adult insect, and the change from the 

 vermiform larva to the winged insect is effected during the 

 period of quiescence which constitutes the pupal stage. Many 

 insects undergo a similar metamorphosis, whilst the young of 

 others are but miniatures of their parents. Intermediate con- 

 ditions between these two extremes are not uncommon, and 

 the variations which the life-history of the various orders of 

 insects present are of use in the classification of this class. 



Order 1. APTERA. 



Characteristics. — Wingless insects whose body is covered with 

 scales or hairs. The segments of the thorax are not fvsed 

 together. The mode of progression is either running, or 

 springing with the aid of an apparatus borne on the ventral 

 side of the abdomen. There is no metamorphosis. 

 The Aptera form the most primitive order of insects. This 

 order consists of a few genera, which are grouped in two sub- 

 orders, (i.) the Collembola and (ii.) the Thysanura, differing 

 considerably from one another. 



Sub-order 1. Collembola. 



The members of this group are widely distributed, but 

 very inconspicuous. Specimens of them may be found under 



