384 ON INCREASE IN SIZE [pt. hi 



mid-increments, represent for each point which begins one period 

 and ends another how much substance the embryo is adding on to 

 itself between the times (a) half-way through the last period, and 

 (b) half-way through the period to come. In other words, the mid- 

 increments convert the daily increments into terms of the points 

 instead of the spaces between the points. If now the mid-increments 



Table 5 1 . Growth of the chick embryo ( White Leghorn) . 

 H. A. Murray's figures. 



are expressed as percentages of their actual weights of embryo at 

 their corresponding points in time, the last column or percentage 

 growth-rate is obtained. This last calculation is, as will be seen, the 

 only one so far made in the table which is open to serious criticism, 

 and it is associated with the name of C. S. Minot, who was the first 

 to propose it as a satisfactory measure of the growth-rate of an 

 organism. When these figures are plotted the curves shown in Fig. 34 

 appear. The actual growth of the embryo expressed in terms of its 



