TIME AND CHANGE 
is typical of the course of the creative energy from 
the first unicellular life up to man, each succeeding 
stage flowing out of, and necessitated by, the pre- 
ceding stage. 
How slowly and surely the circulatory system 
improved! From the cold-blooded animal to the 
warm-blooded is a great advance. In the warm- 
blooded is developed the capacity to maintain a 
fixed temperature while that of the surrounding 
medium changes. The brain and nervous system dis- 
play the same progressive ascent from the brainless 
acrania, up through the fishes, batrachia, reptiles, 
and birds to the top in mammals. The same with the 
skeletons in the invertebrates, from membrane to 
cartilage, from cartilage to bone, so that the primi- 
tive cartilage remaining in any part of the skeleton 
is considered a mark of inferiority. 
According to Cope, there has been progressive 
improvement in the mechanism of the body — it 
has become a better and better machine. The sus- 
pension of the lower jaw, so as to bring the teeth 
nearer the power, — the masseter and related mus- 
cles, — was a slow evolution and a great advance. 
The fin is more primitive than the limb; the limbs 
themselves display a constantly increasing differen- 
tiation of parts from the batrachian to the mamma- 
lian. There was no good ankle joint in early Eocene 
times. The model ankle joint is a tongue and groove 
arrangement, and this is a later evolution. In Eo- 
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