se," remarking (p. 142) that after the more or less
perfect obliteration of the eyes, "natural selection will often have
effected other changes, such as an increase in the length of the antennae
or palpi, as a compensation for blindness," we then summed up as follows
the causes of the production of cave faunae in general:

"1. Change in environment from light, even partial, to twilight or
total darkness, and involving diminution of food, and compensation
for the loss of certain organs by the hypertrophy of others.

"2. Disuse of certain organs.

"3. Adaptation, enabling the more plastic forms to survive and
perpetuate their stock.

"4. Isolation, preventing intercrossing with out-of-door forms,
thus insuring the permanency of the new varieties, species, or
genera.

"5. Heredity, operating to secure for the future the permanence of
the newly originated forms as long as the physical conditions remain
the same.

"Natural selection perhaps expresses the total result of the working
of these five factors rather than being an efficient cause in
itself, or at least constitutes the last term in a series of causes.
Hence Lamarckism in a modern form, or as we have termed it,
Neolamarckism, seems to us to be nearer the truth than Darwinism
proper or natural selection."[222]

In an attempt to apply Lamarck's principle of the origin of the spines
and horns of caterpillars and other insects as well as other animals to
the result of external stimuli,[223] we had not then read what he says
on the subject. (See p. 316.) Having, however, been led to examine into
the matter, from the views held by recent observers, especially Henslow,
and it appearing that Lamarck was substantially correct in supposing
that the blood (his "fluids") would flow to parts on the exposed
portions of the body and thus cause the origin of horns, on the
principle of the saying, "_ubi irritatio, ibi affluxus_," we came to the
following conclusions:

"The Lamarckian factors (1) change (both direct and indirect) in the
_milieu_, (2) need, and (3) habit, and the now generally adopted
principle that a change of function induces change in organs,[224]
and in some or many cases actually induces the hypertrophy and
specialization of what otherwise would be indifferent parts or
organs;--these factors are all-important in the evolution of the
colors, ornaments, and outgrowths from the cuticle of caterpillars."

O