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 Archa^opteryx, these dim 

 reflections seem to have been preserved l)y 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 e!2;,i2;, three weeks are 

 required before the chick is ready to break the shell, yet 

 when incubation has proceeded l)ut eighteen hoiu's, a tiny 

 rod of cells shows where the notochord will be formed — 

 that gelatinous foreshadowing of the back-bone. Thus a 

 character, found firtt in living organisms as high in the 

 scale of life as fish and primitive fish-like creatures, makes 

 its appearance in a few hours, givin<2: 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 



