a study of series of living animals, such as lizards and butterflies, in which the development of a definite scheme of colouration may be followed step by step. Young animals very frequently retain more or less distinct traces of the ancestral colouration, which disappear in the adult, for the development of the individual is, in some respects at least, an abbreviated and condensed recapitulation of the history of the species. In many mammals which, in the adult condition, have a solid body-colour, the young are striped or spotted, a strong indication that these mammals were derived from striped or spotted ancestors. Thus, the Wild Boar has a uniform body-colour in the full-grown stage, but the pigs are longitudinally striped; many deer are spotted throughout life, as in the Fallow Deer, the Axis Deer of India and others, but the great majority of the species, including all the American forms, have uniform colouration, while the fawns are always spotted. Lion cubs
Fig. 5. — Fawns of the Mule Deer (Odocoileus hemionus). Compare with Fig. 83, p. 167. (By permission of the N. Y. Zoölog. Society.)
are also spotted and the adults have a uniform tawny colour, and many such examples might be given.
The study of colouration among existing animals has led to the conclusion that in mammals the primitive colour-
