172 BREEDING 



respects better than tlie tossing of coins. It is done 

 with, counters. Equal numbers of red and white 

 ones are required. Only one pair of characters is 

 being taken into consideration in the case to be 

 illustrated. The female germ cells, half of which 

 bear the dominant member of a pair of factors 

 whilst the other half bear the recessive member, are 

 represented by a collection of 100 red counters (repre- 

 senting the factor for the dominant character) and 

 100 white (representing the factor for the recessive 

 character). The male germ cells, containing similar 

 factors in the same proportions, are represented 

 by a precisely similar collection of red and white 

 counters. 



Three columns are now ruled on a large sheet of 

 paper, to receive the three kinds of couples of counters 

 which can be drawn from these two collections. 

 These three kinds are, of course, red-red, red- 

 white, and white-white. A counter is now drawn 

 at random from one collection, and another counter 

 from the other, and the pair is placed in the column 

 prescribed for it on the paper, according as to whether 

 it is red-red (RR), red-white (RW), or white- 

 white (WW). Another pair is drawn in the same 

 way until, say, a hundred pairs have been placed 

 on the paper. It will be found that the numbers 

 of the three kinds of pairs approximate to the ratio 

 25 per cent. RR, 50 per cent. RAV, 25 per cent. WW. 



The illustrative value of this device may be 

 greatly increased by making it a rule, when a red and 

 a white are drawn together, to put the red on the 



