r, is not true;
climatic and other changes induce corresponding changes in environment
and habit, and these modify the structure of the living forms which are
subjected to them. Indeed, we see intermediate forms and species
corresponding to intermediate conditions.

"To the above causes must be ascribed the infinite variety of existing
forms, independently of any tendency towards progressive
development."[286]

The reader has now before him a fair sample of "the well-known doctrine
of inherited habit as advanced by Lamarck."[287] In what way, let me ask
in passing, does "the case of neuter insects" prove "demonstrative"
against it, unless it is held equally demonstrative against Mr. Darwin's
own position? Lamarck continues:--

"The character of any habitable quarter of the globe is _qua_ man
constant: the constancy of type in species is therefore also _qua_ man
persistent. But this is an illusion. We establish, therefore, the three
following propositions:--

"1. That every considerable and sustained change in the surroundings of
any animal involves a real change in its needs.

"2. That such change of needs involves the necessity of changed action
in order to satisfy these needs, and, in consequence, of new
habits.[288]

"3. It follows that such and such parts, formerly less used, are now
more frequently employed, and in consequence become more highly
developed; new parts also become insensibly evolved in the creature by
its own efforts from within.

"From the foregoing these two general laws may be deduced:--

"_Firstly. That in every animal which has not passed its limit of
development, the more frequent and sustained employment of any organ
develops and aggrandizes it, giving it a power proportionate to the
duration of its employment, while the same organ in default of constant
use becomes insensibly weakened and deteriorated, decreasing
imperceptibly in power until it finally disappears._[289]

"_Secondly. That these gains or losses of organic development, due to
use or disuse, are transmitted to offspring, provided they have been
common to both sexes, or to the animals from which the offspring have
descended._"[290]

Lamarck now sets himself to establish the fact that animals have
developed modifications which have been transmitted to their offspring.

"Naturalists," he says, "have believed that the possession of certain
organs has led to their employment. This is not so: it is need and use
which have