(22) 



race died on August 16, after a period of very hot weather. 



;Vhen selection began, the rr.ear, spine number of the 

 clone was 1.51 spines. The high and low groups therefore 

 consisted of individuals v/ith two or more and one or no 

 spines, respectively. The method of selection was the 

 same as in experiment 1, Although the clone died out be- 

 fore more than one or two selections could be made in most 

 of the lines, Table VI shows that this clone behaved very 

 differently from the one used in experiment 1. The first 

 selection gave a decided difference ( 1.65 spines ) between 

 high and low groups, as against a very slight one in the 

 first experiment ( .22 spines ), And after tlie first se- 

 lection no further result was noticeable. This differs 

 decidedly from the steady progressive effect which was 

 found in experiment 1, 



In both these experiments mass sei.ection was used. 

 In fact, in almost all the experiiT'ents on the effect of 

 selection within pure lines or clones, mass selection 

 exclusively has been used. Mass selection is based en- 

 tirely on the external appearance of the individual, and 

 it is evident that the degree of effectiveness of the se- 

 lection depends very largely on the extent to which the 

 genetic constitution of the individual resembles its ex- 

 ternal aspect. Formerly mass selection within populations 

 v/as extensively practiced, and one of the greatest achieve- 

 ments of the pure line workers has been the pointirig cut 

 that by selecting on a basis of the character of the pro- 

 geny produced by an individual, the same results can be 



