ain the effect as a result of the direct influence of the
environment upon the individual (G. L. L. Buffon), or by the inherited
effects of effort and the use and disuse of parts (J. B. P. Lamarck).
Second, natural selection is believed to have produced the result, and
afterwards maintained it by the survival of the best concealed in each
generation. The former suggestions break down when the complex nature of
numerous special resemblances is appreciated. Thus the arrangement of
colours of many kinds into an appropriate pattern requires the
co-operation of a suitable shape and the rigidly exact adoption of a
certain elaborate attitude. The latter is instinctive, and thus depends
on the central nervous system. The cryptic effect is due to the exact
co-operation of all these factors; and in the present state of science
the only possible hope of an interpretation lies in the theory of
natural selection, which can accumulate any and every variation which
tends towards survival. A few of the chief types of methods by which
concealment is effected may be briefly described. The colours of large
numbers of Vertebrate animals are darkest on the back, and become
gradually lighter on the sides, passing into white on the belly. Abbott
H. Thayer (_The Auk_, vol. xiii., 1896) has suggested that this
gradation obliterates the appearance of solidity, which is due to
shadow. The colour-harmony, which is also essential to concealment, is
produced because the back is of the same tint as the environment (_e.g._
earth) bathed in the cold blue-white of the sky, while the belly, being
cold blue-white bathed in shadow and yellow earth reflections, produces
the same effect. Thayer has made models (in the natural history museums
at London, Oxford and Cambridge) which support his interpretation in a
very convincing manner. This method of neutralizing shadow for the
purpose of concealment by increased lightness of tint was first
suggested by E. B. Poulton in the case of a larva (_Trans. Ent. Soc.
Lond._, 1887, p. 294) and a pupa (_Trans. Ent. Soc. Lond._, 1888, pp.
596, 597), but he did not appreciate the great importance of the
principle. In an analogous method an animal in front of a background of
dark shadow may have part of its body obliterated by the existence of a
dark tint, the remainder resembling, e.g., a part of a leaf (W. Muller,
_Zool. Jahr. J. W. Spengel_, Jena, 1886). This method of rendering
invisible any part which would interfere wi