102 KINSHIP OF BIRDS, AS SHOWN BY EGGS. 
is so variable as to come within no known canon of general- 
ization, for in some cases it seems often reversed, and there 
are, at times, evidences of complete end for end turning of 
the egg. If it be a matter of gland-shape, a constancy of 
physiological structure ought to prevail, which is not justified 
by the various styles of eggs found in a single clutch. If it 
were this, all eggs from the same bird, at least, should be 
alike, or if the markings were made by motion past glands of 
constant dimensions, or outlines, the paths past these glands 
should have a constant width in accord with the direction. 
It would seem, therefore, that any part of the oviducal sur- 
face within which the color is laid on is capable, under 
certain unknown stimulus, of depositing intense color—more 
of the surface at one time, less of it at another. There are 
doubtless times, as shown by solid brownish-colored eggs, 
when the whole surface at once dyes the egg, which was 
quite probably the case originally. As a rule this law holds 
now, that the more variable are the markings, either in shape 
or color, and the more extensive in boldness and number, 
the more variable are the tints of the ground; showing clearly 
that the whole coloring system, from the most remote to the 
most recent, has been thrown into a spasm of variations; 
and that spottings originally came in by the breaking up— 
doubtless often under reverting tendencies—of the bluish 
and brown grounds along with such others as they may have 
combined to produce. The fact that there are some deep 
dark spots on the inside of some eggs may mean that they 
are vestiges of a round of variations that the shell tints 
themselves may have undergone long before they began 
breaking up into specks, spots and blotches. Motion must 
be an element of blotching, but the faintness and intensity 
of these markings varying so much in the same bird, along 
with the variations in their shape, size and number, show 
clearly that it largely depends upon stimulation, and some- 
times, it would even appear, upon the limitations of the sup- 
ply of pigment. 
