evidently akin to each other, furnish at least some indications of the
course of development in the greater systematic divisions, even as the
facts of seasonal dimorphism, mentioned in the last chapter, give hints
as to the course of development in those restricted groups that we call
species or varieties. A brief discussion of the main outlines of the
life-story of insects in the wide, evolutionary sense may thus fitly
conclude this book.

In the first place we turn to the 'records' of those rocks, in whose
stratified layers[12] are entombed remains, often fragmentary and
obscure, of the insects of past ages of the earth's history. Compared
with the thousands of extinct types of hard-shelled marine animals, such
as the Mollusca, fossil insects are few, as could only be expected,
seeing that insects are terrestrial and aerial creatures with slight
chance of preservation in sediments formed under water. Yet a number of
insect remains are now known to naturalists, who are, in this
connection, more particularly indebted to the researches of S.H. Scudder
(1885), C. Brongniart (1894), and A. Handlirsch (1906).

[12] See Table of Geological Systems, p. 123.

We are now considering insects from the standpoint of their
life-histories, and the individual life-story of an insect of which we
possess but a few fragments of wings or body, entombed in a rock formed
possibly before the period of the Coal Measures, can only be a matter of
inference. Still it may safely be inferred that when the structure of
these remains clearly indicates affinity to some existing order or
family, the life-history of the extinct creature must have resembled, on
the whole, that of its nearest living allies. And all the fossil
insects known can be either referred to existing orders, or shown to