238 
COLOUR IN NATURE 
CHAP. 
black spots were produced by accumulations of black 
pigment in the cutis of these regions, in other re¬ 
spects the skin showed no special peculiarities. He 
therefore set himself the problem to find out what 
anatomical or developmental necessities produced 
these aggregations of pigment. 
The ringed snake is marked by three paired 
longitudinal rows of black spots, which correspond 
to the longitudinal lines described by Eimer in the 
wall-lizard, except that in the lizard there is, in ad¬ 
dition, an unpaired median line on the dorsal surface. 
In the embryo at an early stage the surface is marked 
by three pairs of red lines, and a slender median 
unpaired one. The lines are produced by the sub¬ 
jacent blood-vessels and are not necessarily perfectly 
continuous, being sometimes broken into red spots ; 
they are connected with numerous transverse vessels, 
the junctions being marked by distinct swellings of 
bright colour. Of the three lateral lines the median 
is the most distinct, and extends forward in front of 
the eye. A little later the scales begin to develop 
from before backwards, and as they become distinct 
the red lines disappear before them, and, at the same 
time the first traces of pigmentation appear as a 
longitudinal row of pigment spots at each side, 
developed in the position previously occupied by the 
median red line already mentioned. The extension 
of this line in front of the eye is now marked by a 
distinct spot of pigment, which forms a marked feature 
in the adult. The formation of this middle row of 
spots is followed a little later by the appearance of 
two other rows corresponding to the upper and lower 
of the lateral red lines. The first spot of the middle 
