INHERITANCE 



727 



effect in the direction of selection appears. The offspring of the group 

 whose ancestors have had high numbers of spines have a greater average 

 number of spines than the offspring of the group whose ancestors have 

 had low numbers of spines. 



Such results may be illustrated from the clone 326, in which selective 

 breeding for high and low numbers of spines was carried on for a long 

 period (see Table 15). 



Table 15: Early Results of Selection for Low and High Numbers 

 OF Spines, Difflagia corona (from Jennings, 1916) 



In the fourth period there is a distinct difference in the two groups. 

 To test whether this is significant, the fourth period (four months) was 

 divided into six successive periods, and the numbers of spines in the 

 offspring of the two groups determined for each. They were as shown 

 in Table 16. 



Table 16: Later Results of Selection for Low and High Numbers 

 of Spines, D/fflugia corona; Numbers of Spines in the Parents (1-5 

 in the Low Group, 7-11 in the High Group) with the Mean Num- 

 bers OF Spines on Their Offspring in Successive Periods (from Jen- 

 nings, 1916) 



