142
THE ESSEX NATURALIST.
The above considerations of the principal ecological factors
affecting the lives of woodlice have been considered in some
detail because they reveal a most interesting and significant
fact ; namely, that these terrestrial representatives of an
otherwise aquatic group of isopods still seem to find the process
of adaptation to their terrestrial environment to be their greatest
problem, and the lower degree of humidity existing in such
surroundings constitutes their principal controlling factor today—
one of infinitely greater importance to them than the more
usual problem of food supply.
This conclusion places the habits and ways of woodlice in
an entirely new light, and provides a valuable key to the interpre-
tation and understanding of many of the peculiar habits of
these little creatures which otherwise seem strange and un-
accountable. Though so small and insignificant, they are
nevertheless a group of immense biological importance, showing
yet another attempt at adaptation to terrestrial life from an
aquatic ancestry, along lines closely parallel to their more
successful relatives of the Arthropod group, the insects and the
spiders.
The woodlice are still, as it were, in the transitional stages,
however, and it is therefore of particular interest to study them
comparatively and determine how they overcome by gradual
stages such an immense alteration of life, involving not only a
complete change in their feeding habits, but also in their res-
piratory mechanisms and their responses to light and warmth.
V. LIFE HISTORIES.
Although various stages in the lives of woodlice have been
fully and accurately recorded by different writers from time
to time, so far as I know no consecutive account of their entire
life histories has been given ; and since several apparently
new and interesting data have been revealed in the course of my
own investigations, which involved the complete rearing of
between twenty and thirty families of each of the selected
species in the glass observation dishes previously referred to,
it may prove not unprofitable to outline here some sort of
consecutive account of what is known of their life stories.