CHAPTER II 

 RATES OF GROWTH OF INDIVIDUALS 



Tt is difficult to compare with one another the sizes 

 -■-of different individuals, until the changes of size 

 which a single individual undergoes have been recog- 

 nized. There is a progressive increase of mass in the 

 normal life of each individual; this is properly termed 

 growth. Ordinarily between one fission and the next, 

 in the course of vegetative generations, materials are 

 assimilated and size is increased. The rate at which 

 this increase occurs has been studied most extensively 

 in Paramecium. 



1. Paramecium 



The first attempt to find how fast single individuals 

 grow was made by Simpson ('02), who measured with 

 an ocular micrometer the length and the breadth of 

 living Paramecium caudatum. He isolated grown 

 individuals which showed signs of constricting into 

 two; and timed exactly when fission became complete. 

 Each member of the daughter pairs thus produced was 

 measured twice; first a few hours after fission and 

 again many hours after fission. In all of the scores of 

 individuals, some increase in length and in breadth oc- 

 curred. But it is the mass or volume of the body rather 

 than any one dimension which best measures growth, 

 and therefore it is necessary to attempt, however ques- 

 tionably, to estimate volume from the length and 

 breadth which were the actual data. To derive any- 

 thing far-reaching from the measurements of protista, 

 we are forced to make free with them to the extent of 

 calculating volumes in ways which are not rigorously 

 justified. For Paramecium it is best to consider the 

 volume of the body as proportional to length X breadth 



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