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rudiments of the cerebro-spinal axis and of the vertebral column 
after thirty-six hours' incubation. 
(a) Nota primitiva 
80. The outer circle represents the boundary of the yolk ; 
but I must fix attention on the central streak,, which is destined 
to become the foundation of the living structure. All that we 
have been considering simply subserves the development of this 
little streak, and all is swallowed up in the course of its ex- 
tension into the perfect chicken, and, as every one knows, 
nothing but the broken shell remains when that has emerged. 
All the rest has been simply predestined to subserve this 
purpose. 
Contrast. 
81. Now I would ask what resemblance can the most exalted 
scientific imagination detect between this and the aggregation 
of atom to atom, and of molecule to molecule, in crystallization ? 
Development. 
82. It would prolong to an unreasonable length, though it 
might strengthen the argument of this paper, to consider the 
further development of living creatures from the embryo; but 
I hope I have made it quite evident that, in place of chemical 
affinities binding atom to atom and molecule to molecule, 
acting with mathematical precision, at inconceivably small dis- 
tances and on particles of matter inconceivably minute, we 
have, before we can account for the phenomena of life, to find 
out the formative power;* which, working from the invisible, 
and being itself imponderable, can guide, control, coerce, or, if 
* “ En resume, il existe dans tout le regne organique une puissance 
formative, qui, dans le regne vegetal, agit principalement d’une maniere 
symetrique, puis, en outre conformement a un certain but ” — Link, Recherches 
