513 JENNINGS— HEREDITY IN PROTOZOA. [April 24, 



sion of different lines or races, even if conditions of growth and 

 environment are essentially the same, may give us, as we have seen, 

 mean lengths of somewhat less than 100, or somewhat more than 

 200 microns, or any intermediate length. Different stages in growth 

 ma}' give us, in the same line and in the same environment, means 

 differing to such an extent that one is nearly twice the other, or any 

 intermediate condition. The absolute extreme values will, of course, 

 depend upon the race employed ; in the line i the variation of mean 

 length caused by growth might be from about 50 to about 100 

 microns ; in D it was from about 100 to about 200 microns ; in L it 

 would be from about 117 to 234 microns. Different environmental 

 conditions give us, within the same lines, mean lengths differing to 

 such an extent that the greater is 25 to 30 per cent, more than the 

 less (lines c and D). In different "wild" cultures we shall have 

 different combinations of all these factors, resulting in extreme 

 diversities in different cases. Fig. 7 shows two extreme sizes drawn 

 to the same scale (page 496). 



2. The various different breadths depend upon the same factors 

 as the different lengths. There are certain differences, however. 

 As compared with length, the breadth is affected much less by 

 growth; about the same (though a trifle less) by diversity of race; 

 and much more by environmental differences. Environmental dif- 

 ferences produced within the races D and c such differences in mean 

 breadth that the greater was about twice the less. 



3. The observed variation, as measured by the coefficient of 

 variation, of course, depends upon the three sets of factors enumer- 

 ated above as affecting the length and breadth. If a collection 

 consisted of several different lines or races, all in the same condition 

 as regards growth and environmental conditions, this would, of 

 course, give us a considerable coefficient of variation. For example, 

 if a collection consisted of ten individuals each of all the different 

 lines represented in Table XXVI., page 502, and if all of each set of 

 ten had the mean dimensions for its line (thus excluding differences 

 due to growth and environment within the lines), the coefficient of 

 variation when computed in the same way as for the actual collections 

 given in the text is found to be for length 19.689; for breadth 15.679. 



If a collection consists of individuals all belonging to the same 



