420 Marion L. Durbin 
throughout the regenerative period. Four kinds of change in rate 
can be distinctly recognized. 
3 The operation is followed by an interval of low rate, succeeded 
by one of rapidly increasing rate, then by one of rapidly decreasing 
rate and finally an interval in which the rate gradually approaches 
zero. 
4 The first low period is explained by the combination of two 
factors, (a) the shock of the injury and (4) the formation of a cap 
of embryonic cells which is to serve as a basis for the more active 
regeneration. : 
5 The second or period of rapidly increasing growth is the one 
in which practically all the cells in the new part are undifferen- 
tiated and are rapidly dividing. 
6 The third and fourth periods are explained by the appear- 
ance of differentiation which lessens the number of dividing cells. 
7 The curve representing these changes in. the rate of regener- 
ation agrees in general features with the curve of growth as de- 
scribed by Minot and others. 
8 The above points strongly support the view that the essen- 
tial factors controlling growth and regeneration are similar. 
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Davenport, C. B. ’99—Experimental Morphology, Part II, New York. 
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Minor, C. S. ’o8—Age, Growth and Death. New York. 
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SPALLANZANI, Lazaro ABBE, 1769—An Essay on Animal Reproductions. 
