GROWTH 523 



logarithmic growth is more rapid in the data from Jennings's measure- 

 ments; however, his animals continued to grow for a longer period and 

 reached a slightly greater length than did those measured by Mizuno 

 and Popoff. The variations may be due to differences in nutrition or to 

 race. The results are all in terms of averages from diiferent animals, 

 and do not show the continuous change of size of a given animal. This 

 type of averaging of cross-sectional data is known to give variation. 



The measurements of breadth (Fig. 131) are not as consistent as 

 those of length. With the exception of one of Estabrook's series, the 

 breadth decreases following fission, and growth in this dimension com- 

 mences later, in the measurements given. Thickness and breadth meas- 

 urements, plotted from Popoff's observations, show no change in size 

 for the first two hours. The lack of agreement of the different series of 

 measurements suggests differences in the pattern of growth for the 

 different races. Growth in thickness occurred later than growth in breadth 

 with Popoff's P. caudatum. 



Growth in area (Fig. 130) is negative during the time that the 

 breadth is decreasing, after which the increase continues for most of the 

 cycle at about the same relative rate. Growth in volume, from Popoff's 

 calculations (Fig. 132), does not show the early negative phase, because 

 his animals apparently did not change form during division as the oth- 

 ers did. With minor fluctuations the increase in volume continues in a 

 suitable environment until the time of the next fission. 



The growth of Paramecium auvelia (Fig. 132) , plotted from the meas- 

 urements of Erdmann (1920), is quite similar to that of P. caudatum. 

 Erdmann's three races differed from one another in size. No decrease 

 in breadth was reported for this species. 



The growth in volume of the first individual and its progeny is given 

 in Figure 132 for the soil amoeba, Hartmanella hyalina (Cutler and 

 Crump, 1927) . The growth curve is very similar to that of P. caudatum. 

 Ten drawings were made rapidly at each time, and the volume was ob- 

 tained from the average areas, on the assumption that the animals were 

 1 |j thick. The temperature was 21° C. The growth in volume of Amoeba 

 proteus was measured by Chalkley (1929). The animals were pipetted 

 until they assumed a spherical form, and the diameters of the cell and 

 nucleus were then measured. The growth of the Amoeba is slow, and 

 Chalkley's observations were not continued until the equilibrium size 



