121) 



began. On December 14 an epidemic of sexual reproduction 

 put an end to the experiment. 



In thiis experiment simple mass selection was used. 

 The clone was divided into t7/o parts, the individuals with 

 six or more spines being classed as high, those with five 

 or less as low. In each group only those progeny whose 

 spine numbers lay on the same side of the mean ( 6.56 spines) 

 as their parent's were allowed to reproduce. 



As Table V shows, the difference in mean spine number 

 between the progeny produced by the hlg?i and low groups 

 was only .2'c of a spine after the first selection, but 

 rose to 1.61 spines after the second, and to 2.26 spines 

 after the third. Apparently, then, in this clone, three 

 selections sufficed to isolate within the clone high and 

 low strains with a mean spine number of about 7.75 and 

 5.5 spines, respectively. This quick and decided effect 

 of selection was most unexpected, and it is most unfortu- 

 nate that the onset of sexual reproaucLion ended this ex- 

 periment so prematurely. The num.bers involved are too 

 small to allow of any definite conclusion from an exper- 

 iment of such short auration. 



Selection experiment 2. In Table VI is shown the 

 course of a similar experiment in a clone with lewer spines 

 and of larger size. The progenitor of this clone was 

 isolated on July 3, 1915, from among aLgae attached to a 

 deaa stick in an irjlet of I-obska pond near V.'oods Hole, 

 Mass. Selection was started or- July 28, when tne clone 

 contained 55 individuals. The last individual of this 



