An Introduction to a Biology 



may be imitated by pouring equal numbers of red and white 

 counters into some convenient receptacle. Now let us pair 

 two such imitation hybrids, using for tliis purpose two bags 

 or hats, each containing equal numbers of red and white 

 counters. Two vertical lines are drawn on a large sheet of 

 paper ; the space between the lines being reserved for pairs, 

 each consisting of a red and a white (RW) ; the space on 

 one side of the two lines for two reds {RR), and that on the 

 other for two whites (TF Tf). A counter is taken at random 

 out of one hat ; then another out of the other hat ; and the 

 pair, according to its character (RR, RW or IF IF), is assigned 

 to the column, on the paper, prepared for it. We should, 

 of course, expect in a large number of trials that there would 

 be 25% RR, 50% RW, and 25% WW ; this is, in fact, what 

 happens. Now in playing this game there is only one rule 

 to be observed, which is, " When a red is drawn with a white 

 the red shall he placed on the top of the white^ (It is this 

 rule that confers whatever usefulness there is in this device.) 

 Let us make fifty draws and place the result on the paper : 

 the outcome of such a trial taken as I write is 13 RR, 26 

 RW, and 11 TFTF ; which, for the smallness of the number 

 drawn, is not a bad approximation. Let that colour repre- 

 sent the dominant character, which was placed uppermost 

 in the i^TF's ; let W be the recessive and RW the hybrid ; 

 the observance of the only rule of the game brings out the 

 fact that in the hybrid it is the dominant character which 

 is manifested, while the recessive is hidden. Now, in placing 

 the RW^& on the paper one is not likely to absolutely con- 

 ceal the white ; so that, while from our rule we realise that 

 red is the character which the hybrid bears, we are pre- 

 vented (by the fact tliat the white is not absolutely con- 

 cealed) from forgetting the real constitution of the hybrids 

 (or rather their gonads), namely, that they contain germs 

 representing respectively dominant and recessive characters 

 in equal numbers. It will be seen from this illustration 

 that, in making the living cross, all that is done is to mingle 



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