- Outline of Male (a') and Female (?) Cockroaches (Blatta) from the side, showing Abdominal Segments (numbered I-b).
In the Mesozoic rocks (Trias and Lias) there have been discovered remains of insects intermediate between those ancient forms and our modern cockroaches, the differentiation between forewings and hindwings having begun.
Smaller appendages (such as the stylets of male cockroaches) may be carried on the ninth segment.
Insects are numerous, and of about 500 species of beetle some 80% are not known to exist elsewhere; cockroaches and green locusts are pests, as are, also, mosquitoes,' wasps, scorpions, centipedes and white ants, which have all been introduced from elsewhere.