TIME AND CHANGE 
climbing vines find their support, because in the 
same blind way they feel in all directions. Plants 
and animals and races of men grope their way to 
new fields, to new powers, to new. inventions. 
Indeed, how like an inventor Nature has worked, 
constantly improving her models, adding to and 
changing as experience would seem to dictate! She 
has developed her higher and more complex forms 
as man has developed his printing-press, or steam- 
engine, from rude, simple beginnings. From the 
two-chambered heart of the fish she made the treble- 
chambered heart of the frog, and then the four- 
chambered heart of the mammal. The first mam- 
mary gland had no nipples; the milk oozed out and 
was licked off by the young. The nipple was a great 
improvement, as was the power of suckling in the 
young. 
Experimenting and experimenting endlessly, tak- 
ing a forward step only when compelled by neces- 
sity,— this is the way of Nature, — experimenting 
with eyes, with ears, with teeth, with limbs, with 
feet, with toes, with wings, with bladders and lungs, 
with scales and armors, hitting upon the back- 
bone only after long trials with other forms, hitting 
upon the movable eye only after long ages of other 
eyes, hitting on the mammal only after long ages 
of egg-laying vertebrates, hitting on the placenta 
only recently,— experimenting all around the circle, 
discarding and inventing, taking ages to perfect 
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