XI 
THE COLOURS OF AMPHIBIANS 
231 
difference expressing itself especially in diminished 
brightness of tint and in the absence of the cuticular 
modification which gives rise to a blue colour. 
Relation of Larval and Adult Coloration 
It is unfortunate that the paucity of observations 
makes us unable to say much on this interesting 
subject, but the statements given above suggest one 
or two points. 
First as to the position of the pigment and its 
meaning. We have seen that the dark pigment, 
both in adult and in larva, occurs to a slight extent 
in the epidermis, and much more markedly in special 
pigment cells in the dermis or true skin. The 
epidermis, with its contained pigment, is periodically 
cast and renewed, so that there must be a slow 
elimination of pigment from the body in this way. 
We have already seen that it is most probable that 
the pigment originates in the dermis or deeper tissues, 
so that there must be a continual migration of pig¬ 
ment from the dermis to the epidermis. Such a 
state of affairs occurs very frequently in vertebrates, 
and is, as noted above, often regarded as a proof that 
the coloration is the result of an excretory process. 
The development of the coloration, as already 
described, supports this theory in so far as it tends 
to show that the dark pigment usually increases in 
amount during growth, and that it tends to be more 
abundant in males than in females, in normal indi¬ 
viduals than in those which are precociously sexual. 
The proof would, however, be more cogent were it 
not for the presence of. the lipochromes. These can 
