150 
ORNITHOLOGIST 
[Vol. 11--No. 10 


egg is exposed and the intensity of its pigmenta- 
tion; that direct exposure to the sun’s rays is 
necessary for pigment to acquire its full develop- 
ment; and that eggs deposited in sites protected 
from the sun’s rays gradually lose their pigment 
layer. 
If we examine these three shades from a purely 
chromatic standpoint, apart from any physiologi- 
cal views of their development, we shall see how 
admirably adapted they are for the purposes of 
protection and concealment. 
1. Green is the colour we would natually ex- 
pect to find used as a protection for eggs. We 
know by experience that it has a peculiar soften- 
ing influence on light. When it is present, it is 
always as aground tint, uniformly spread over 
the surface of the egg. Most eggs are more or 
less covered with spots, blotches, or streaks, but 
these markings are never formed of green pig- 
ment. Many markings appear green to the eye, 
but this appearance is produced by the green 
gound tint being seen through a thin layer of 
black or brown. The spots in that case are of a 
darker green than the ground, but never deeper or 
richer. The most common tint is a bluish-green. 
2. Red. If we see a reason for the use of 
green pigment as a protective layer on eggs, we 
can find an equally good one why red should be 
employed as the second or supplementary colour. 
In the chromatic circle all colours are arranged in 
pairs, and the colours in every pair are comple- 
mentary to each other. When two colours are 
seen in juxtaposition, they mutually effect each 
other, both in colour and tone. A yellow object, 
for example, placed close to a blue one, will ap- 
pear as if inclined to orange, while the blue ob- 
ject will seem to incline towards violet. But two 
complementary colours, such as red and green, do 
not modify one another’s colours by contiguity. 
They merely enhance each other’s characteristics. 
Further, Professor Church remarks that green 
and red have a relation to each other which is 
different from that of any other pair of colours. 
‘That there is something very peculiar in the re- 
lation of green to red,” he adds, “may. also be 
concluded from the frequency with which there 
two colours are confounded by persons who suffer 
from colour blindness.” The exact tint, which 
seems to be the basis of all the reds and browns 
found on eggs is a russet or orange-brown, and, 
if we examine the chromatic circle of Maxwell, 
this tint will be seen to be the complementary 
colour of the bluish-green, which I have just re- 
marked is_the usual ground tint. Red pigment is 
usually arranged in the form of spots, streaks, or 
blotches. Occasionally it is used as a ground tint 
—as in the Grouse tribe—but then it is usually 
more or less speckled. It rarely if ever exhibits 
the smoothness or evenness of the green. 
3. Black seems to be employed mostly as a 
tone-giving neutral to inhance these two colours. 
Orange or red seen in juxtaposition with black is 
rendered rather lighter in tone and more lumi- 
nous; green with black becomes more brilliant, 
but the black suffers in purity, and appears 
slightly tinged with a ruddy hue. The grey 
markings seen on many eggs, ¢. g., the Sparrow 
tribe, are produced by a light layer of black pig- 
ment. 
Next to their limited range the variation of the 
colours of eggs in the same species is the most 
striking characteristic. In the eggs of several 
species, as Gulls, Terns and Guillemots, the range 
of colours extends almost from one end of the 
scale to the other. What a contrast with the 
colours of the birds themselves, where the colour 
of a few feathers in some instances constitute the 
difference between the species, or with lepidoptera 
where the pigmentation of afew scales determines 
the name of the insect. And not only do the 
eggs of birds of the same species differ, but those 
of the same individual vary almost to the same 
extent. Thus in a Tern’s nest, containing four 
eggs. I found one of a pale green colour and 
another of a deep reddish-brown. The other two 
were of intermediate tints. In this case the 
green egg had been the first laid and the brown 
one last. 
Basing our theories on the development of pig- 
ments referred to above, which is generally ac- 
cepted by physiologists, we would infer that 
green was the first colour which was developed 
in the eggs of the early species of birds. The 
eggs of the species extant support this conclusion. 
Green is the most common and most widely dis- 
tributed colour. Schmidt states: ‘The more 
stubbornly a character is transmitted, or, what 
amounts to the same, the greater the number of 
families, genera, and species over which a charac- 
ter is extended, the earlier did it appear in the 
ancestral stock.” It is also, as has been shown 
previously, the colour best adapted for protection 
from the stimulating influence of the sun’s rays, 
and there can be no doubt but that this is the 
primary use of pigment. Almost every egg which 
is laid in a situation where there is no need of 
concealment, but which is exposed to the sun’s 
rays—é. g., Rooks, Herons—is of a green colour. 
Red or russet, and all the intermediate tints, ap- 
pear to be developed chiefly for concealment, the 
different shades of brown showing in many in- 
stances perfect adaption of the colour of the egg 
with that of its surroundings. This colour is 
