The Bird in the Egg 471 
a spark of life reflected from the far-distant past shines forth 
so vividly as to hold us spellbound, almost instantly to 
fade out forever, having no part in the actual life of the 
chick. Like the finding of the Archzeopteryx, these dim 
reflections seem to have been preserved by some kind 
Providence, especially to aid our groping efforts to find 
the truth of ages that are past. Were it not for these 
we should never dare to voice such an incredible theory 
as the story of evolution would be, were it not supported 
by unanswerable proofs. The question which interests 
scientists to-day is not whether evolution is true, but how 
its processes and changes have been brought about. 
The difficulty of seizing upon these evanescent bits of 
realism of the past will be appreciated when we know 
that while, in the case of the hen’s egg, three weeks are 
required before the chick is ready to break the shell, yet 
when incubation has proceeded but eighteen hours, a tiny 
rod of cells shows where the notochord will be formed— 
that gelatinous foreshadowing of the back-bone. Thus a 
character, found first in living organisms as high in the 
scale of life as fish and primitive fish-like creatures, makes 
its appearance in a few hours, giving but the scantest 
opportunity for the passing in review of embryonic features 
of the great group of invertebrates, or those animals, like 
starfishes, crabs, worms, and insects, which lack a back- 
bone. 
The simplest way to study the growing embryo is to put 
a number of eggs in an incubator, or under a hen, and 
examine one on each successive day. If the egg is held 
firmly, by pressing it down into a box of loose sand, the 
