60 



CELL-DIVISION AND GROWTH 



II. 2 



take place during growth in the rate of growth itself, in the 

 variability of the organism and in the magnitude of the correla- 

 tions between its various parts. 



TABLE I 



Showing the percentage of water in Chick embryos at various stages up 

 to hatching. (From Davenport, 1899 (2), after Potts.) The table also 

 shows the hourly and daily percentage increments of weight. 



TABLE II 



Showing the percentage of water in the Human embryo at various stages 

 up to birth. (From Davenport, 1899 (2), after Fehling.) The table also 

 shows the weekly percentage increments of weight. 



Weekly per- Percentage 

 centasre increment, of water. 



Increase. 



35-525 



635 

 142-0 

 327-0 

 355-0 

 40 

 712-0 



331-2 

 34-8 

 71-0 

 67-6 

 15-6 

 0-1 

 19-2 



97-5 



91-8 

 92-0 

 89-9 

 86-4 

 83-7 

 829 

 74-2 



We follow Minot and Preyer in measuring the rate of growth 

 by the percentage increments of weight (or of other measure- 

 ments where weight is not available) during a given interval of 

 time ; that is to say, by expressing the increase in weight during 

 a given period as a percentage of the weight at the beginning 

 (or end) of that period. The change of rate, if any, is found 

 by taking such percentage increments for successive equal 

 increments of time. 



As a first example let us consider the data furnished by Minot 



