ceeded in rearing an albino, though there was less light in his
laboratory than in that of Koelliker, and his axolotls came from the same
stock. Bert made the mistake of confounding albinism with the phenomenon
of etiolation in plants; in fact, he gives the name "etiolation" to the
albinism noticed in his axolotls.[95]

[94] Semper, _Animal Life_, p. 93.

[95] _Ibid._, p. 88 _et seq._

There is a marked difference between the functions of the chlorophyll
bodies found in plants and the chromatophores found in animals. The
former play one of the most important roles in the drama of plant life,
inasmuch as they subserve a vital function, while the latter act a minor
part, because they serve only as an instrument or means of protection.

Light is of great importance in its influence on chlorophyll, which is a
microscopic, elementary body on which the vital strength of the plant
depends, while it is not at all necessary to the chromatophores,--cell
bodies secreting pigmentary matter for the purpose of protection. Of
course, when animals are subjected to darkness for very long periods of
time, the chromatophores are modified, and, sometimes, are wholly
obliterated. They follow a well-known natural law, which declares that,
when a function of an organ is no longer of any use to an animal, both
organ and function become rudimentary, and finally disappear.

Many animals live for generations in total darkness before losing their
pigment. I, myself, have seen black beetles in Mammoth Cave, Kentucky,
in the neighborhood of Gorin's Dome, which is far within the depths of
the cave. As beetles rarely range over a hundred yards from their place
of birth, these insects must have been born in the cave and reared in
the dark.

When speaking of light, if not otherwise specified, I mean diffused
daylight which carries no heat rays. I believe that heat is a prominent
factor in the production of color; the discussion of this point,
however, does not properly belong to the subject under consideration.

Some experiments on newts, made by myself several years ago, show that
the absence of light does not influence pigmentation,--that is, through
several generations. My animals were kept under observation from the
extrusion of the eggs until full maturity had been reached, and great
care was taken to make experiments as accurate and as conclusive as
possible.

Those reared in total darkness or in a red light were always
dark-colored;