THE PURE LINE 111 



other in size, structure, physical character, and rate 

 of niultiphcation as well as in the environmental 

 conditions required for their existence and, further- 

 more, that these differences, in an hereditary sense, 

 are "as rigid as iron." 



With respect to the character of mean length he 

 was able to isolate eight races, or pure lines, whose 

 average size, drawn to scale, is shown in Figure 37. 



256 < MICRA > 



Fig. 38. — Diagram of a single race (D) showing the variation in the size 

 of the individuals. Magnified about 230 diameters. After Jennings. 



Each of these pure lines produced a progeny 

 which exhibited a considerable range of fluctuating 

 variation. The offspring of pure line D, for example, 

 varied from ^56 to 80 micra ^ in length with an aver- 

 age of 176 micra, as shown in Figure 38, where samples 

 of the different classes of variants in pure line D are 

 arranged in a series. 



A single representative of each of the different 

 classes of variants out of all of the eight pure lines 

 bred by Jennings is shown in Figure 39. 



Each horizontal row represents a single race or 



^ A micron is jo^o^th of a millimeter. 



