THE PURE LINE 113 



numerous near the average for that line and less 

 numerous at the extremes, thus forming the typical 

 normal frequency polygons of fluctuating variability. 

 The significant fact about these series is this, that 

 extreme individuals selected from any pure line do 

 not reproduce extreme sizes like themselves, but 

 instead, a progeny varying according to the laws of 

 chance around the average standard of the particular 

 line from which it came. 



8. PHENOTYPICAL AND GENOTYPTCAL DISTINCTIONS 



From the foregoing it will be seen that the be- 

 havior of an organism in heredity cannot always 

 be determined by an inspection of its somatic char- 

 acters alone. 



For example, six Paramecia, each 155 micra in 

 length and apparently identical, could be selected 

 from the six upper pure lines in Jennings' table given 

 in Figure 39 which would produce six progenies 

 definitely unlike, whereas in the case of pure line D, 

 twenty-four Paramecia, all measurably different 

 from each other in size, would be found to produce 

 twenty-four progenies practically identical. 



Organisms that appear to be alike, regardless of 

 their germinal constitution, are said by Johanssen 

 to be identical phenotypically , or to belong to the 

 same phenotype. 



On the other hand, organisms having identical 

 germinal determiners such as those of the varying 

 members of pure line D, are said to be genotypically 

 alike or to belong to the same genotype. 



