PARENTAL COLOUR 93 
young animal, or an adult, are of two kinds— 
(1) structures, or parts of structures, which 
their ancestors possessed, and which have 
been retained because they are useful; (2) 
added structures, which their distant ancestors 
never possessed, to fit some new environment ; 
these may be added at any stage of develop- 
ment from the egg to the complete adult. 
Therefore the hereditary explanation of the 
difference of colour between young and adult 
is not sufficient. That this is so is also proved 
by the whole of experimental embryology, and 
also by the fact that examples can be found 
of young animals not presenting protective 
colouring, and almost certainly not having the 
colour of their ancestors. One must conclude, 
therefore, that young animals are as a rule 
protectively coloured, and adults often con- 
spicuously coloured, for a purpose. 
An examination of the species which present 
protectively coloured young and conspicuously 
coloured adults, reveals the fact that in the 
vast majority of cases young and parents are 
associated together during a portion of their 
lives; and further, that it is whilst thus 
associated that the difference is most marked 
—e.g. parents are most brilliant during the 
breeding season. Examples of conspicuously 
