HEREDITY OF HAIR-LENGTH IN GUINEA-PIGS. II 



than either of the others, though the increase over the last mating is not a 

 very striking one, and several individuals were just on the line between 

 C and D, so that little stress can be laid upon the classification made. 



(e) MATING B(D) [FROM Two SUCCESSIVE CROSSES WITH D] XD. 



If two crosses introduce greater contamination of the gametes than 

 one, then the C and D classes resulting from this cross should be high at 

 the expense of the B class. The observed result accords with this inter- 

 pretation, though the number of young produced is not large. There were 

 one B, three C and five D offspring. 



The question now arises, What is the nature of the C individuals ? Are 

 they the result of partial reversal of dominance, so that when B meets D in 

 fertilization there is produced an intermediate condition, or have B and D 

 actually fused to form something different from either ? Matings of C indi- 

 viduals among themselves or with B and with D respectively should throw 

 light on this question. If C individuals result merely from partial arrest 

 of the dominance of B, we shall expect C to split at gamete formation into 

 B and D. If it does not do this we may conclude that it represents a firm 

 union of B and D to form a new character, C. 



(/) MATING C(>?) XD. 



This mating produced a mixture of C's and D's, in all eight C, nine D 

 and five individuals of undetermined character. Apparently the C's used in 

 this experiment were heterozygous, producing some C and some D gametes. 

 The former, combined with D gametes, produced C individuals ; the latter 

 similarly united produced D individuals. The fact that no B offspring were 

 produced indicates that the C parents did not form B gametes. We con- 

 clude that the C gamete is probably a new creation due to a partial and 

 permanent blend of B with D. 



(g) MATING C(D) [PRODUCED BY Two SUCCESSIVE CROSSES WITH D] XD. 



This mating should yield a larger proportion of D offspring than the 

 last, if cross-breeding introduces contamination of gametes. The observed 

 result was nine C, eighteen D and six young of undetermined character, 

 which result supports the hypothesis stated. It should be said that in this 

 mating, as in those previously described, the classification of the offspring 

 was wholly unbiased, as it was in each case made before the animal's ped- 

 igree was looked up to see in what group of offspring the individual in 

 question should be placed. It must be borne in mind, however, that the C 

 group it not a natural one to be considered a unit-character by itself. It 



