INFLUENCE OF AGE ON PIGMENTATION. 
328 
with orange, with grey lateral handings, before again eventually 
reverting to the orange-yellow colour which distingui.shed it when 
tirst found. 
riginent may be a natural product of the organism, or an inherent 
characteristic of the substances composing the body, as exemplified by 
the dee[) dull red colo\ir of hamiatin, the base of luemoglobin, and 
therefore not dependent on the action of light, which is not really 
essential to its i)roduction, as is demonstrated by the varied coloura- 
tion of the internal organs and l)y the brilliant tints of many deep sea 
animals which permanently dwell in cimmerian darkness. Its distri- 
bution and arrangement is, however, largely intinenced by selective 
and other forces, and also dependent on the character of the tissues 
and the nature of the genend environment, being modified by age, the 
amount of heat or cold, moisture or drought, food, light or darkness 
or, in fact, by anything which affects the i)hy.sical constitution of the 
body and may by retarding or accelerating chemical changes or com- 
binations produce changes of colour. 
Age has great inflnence on colouring, Linuu' fhcvtis and other 
s[)ecies becoming darker with advancing age, and this chrumological 
change assists ns to a better understanding of a i)robably more primi- 
tive colouring, as the accepted law of coloration in animals is for the 
young of allied species or genera to bear more resemblance to each 
other and to their common ancestor than the adults do, the succes- 
sive changes undergone during growth probably hinting at the series of 
adaptations necessitated by environment during their .specific life. 
In Arl<iii nuniiitns, one of fhe most primitive species of that genus, 
a greeni.di tint is indicated by its early develoi)ment, as jn-obably an 
ancient colouring of that sjjecies, this colour changing from time to 
time during growth, through yellow with slate coloured dorsal and 
lateral lines, to nearly uniform yellowi.^h-white before finally becoming 
grey on the hack, with greyish-yellow sides and yellower caudal region, 
the mantle assuming a somewhat uniform dull greyi.sh-orange colour. 
Arldii <(tcr has also been noted to undergo even more remarkable 
and varied colour changes during growth, both probably imlicating 
adaptations to stations succe.ssively occupieil during the extension of 
their range, the observed scale of changes undergone in dermal 
cobnation by the Arions and other gToui)s thus suggesting the i)robable 
route of their evolution to the attainment of their ju’esent tints, and 
although the genetic .sequence of colours in the mollusca has not yet 
