Rates of Growth of Individuals 19 



X breadth. From the data of Simpson one arrives at 

 the result that the growth, in length, in breadth, and 

 in volume, was greater in the period from 14 to 33 

 hours than in the period from 6 to 26 hours after fis- 

 sion. As we shall see, larger numbers of measurements 

 and more constant environmental conditions are 

 necessary adequately to estimate growth. 



Jennings's data. Jennings ('08b) studied the 

 growth of Paramecium caudatum, using very large 

 numbers of individuals. To obtain accurate measure- 

 ments he killed and fixed the individuals at known 

 times after fission ; he demonstrated that the specimens 

 fixed by his method did not change in size from the 

 living. The length and breadth of each was recorded, 

 from which frequency distributions and averages were 

 obtained at each of several periods of time. Alto- 

 gether, adequate data for the dimensions of the body 

 were obtained at ten periods during the growth cycle. 

 All the individuals measured were originally derived 

 from a single parent, and thus belonged to one clone; 

 but it was advisable to correct, because variations oc- 

 curred in the medium furnished, in order to compare 

 different cultures and different days. The corrected 

 results so obtained, based on 769 individuals, are repre- 

 sented in figure 6. 



In these Paramecia, the breadth changed very little 

 throughout the generation cycle, so that the length 

 and volume were roughly parallel. But just before 

 fission there was a sudden shortening, and just after 

 fission an equally sudden lengthening of the body. It 

 is obvious, therefore, that it would be unjustified either 

 to consider the volume as always proportional to 

 length or'to consider the volume as always proportion- 

 al to the cube of length. 



Estabrook ('10), working in Jennings's laboratory, 

 also studied the growth of individual Paramecium cau- 



