In Arachnida, Myriapoda, and probably also Insecta, the body cavity is primitively prolonged into the limbs.
Why it is, in the Insecta, that islands should predispose to an apterous state more than continents, it is not easy to speculate.
Among tracheates, the Chilopoda are certainly more closely allied to the Insecta than are any other wingless forms.
But facts like those are, after all, nothing more than such as we may trace the counterpart of in higher animals than the Insecta.
The behaviour of some Insecta points strongly to their possessing memory, rudimentary in kind though it may be.
On the other hand, we certainly cannot regard the Collembola as a group equivalent in value to the Insecta.
It is estimated that four-fifths of the species comprised within the animal kingdom belong to the class of the Insecta.
It was thus reduced by Lamarck in area, and made to comprise only the six-legged, wing-bearing “Insecta.”
The best known examples of this form of alternations of generations are found amongst the Insecta.
It treats of curious animals which the author considers as more nearly allied to the Insecta than to the Crustacea or Arachnid.