bo 
ZOOLOGY 
Os 
Os 
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 example 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. 
Orper 1. APTERA. 
CHARACTERISTICS.— Wingless insects whose body is covered with 
scales or hairs. The segments of the thorax are not fused 
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 (i1.) 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 
