344 THE AMERICAN NATURALIST [Vol. XLTI 



gether. Expectation in this case is 25 per cent, of the 

 straight hair and 75 per cent, of the curved types— of the 

 later 25 per cent, being pure dominants (DD) and 50 per 

 cent. DR. Of 59 offspring of two DR parents there were 

 actually found 22 per cent, curly, 51 per cent, wavy and 

 27 per cent, straight, or 73 per cent, curved to 27 per cent, 

 straight. This again accords closely with expectation 

 and supports the view of the essential DR nature of wavy 

 hair (Cf. Bar., Gav., Gen. families). 



All results indicate with a high degree of probability 

 that straight hair is recessive to spiral hair; but it is 

 probable that the spiral form may, in some cases, fail 

 to dominate. 



We have now to consider the behavior of wavy in rela- 

 tion to curly or kinky, i. e., the lesser grade toward the 

 greater. The statistics show clearly that wavy hair is 

 usually, if not always, a heterozygous condition, and not 

 merely an intermediate stage that is recessive to a higher 

 stage (curly) and dominant over a lower (straight). For 

 straight by wavy frequently gives curly (10 per cent, of 

 cases) as well as wavy and straight. The result is in 

 close accord with the conclusion that wavy always carries 

 both straight and curly germ cells and when mated with 

 single yields in the offspring an equality of straight and 

 curved hair. Thus 113 offspring of straight by wavy 

 parents give 54 per cent, straight and 46 per cent, curved 

 hair. The "curly" germ cell of a ivavy-hsared person, 

 uniting with a "straight" germ cell, usually gives the 

 heterozygous, wavy form ; but in 23 per cent, of the cases 

 fails to do so, owing, we may say, to the unusual activity 

 of the curly determiner. Wavy appears also when the 

 curly germ cells of a heterozygous curly -la aired person 

 unite with "straight" germ cells. As in the last case, 

 the offspring are not all wavy; indeed, the proportion of 

 wavy is less, for 53 per cent, of the offspring are curly. 

 That peculiar strength which makes a heterozygote curly 

 instead of wavy tends to make its heterozygous offspring 

 also curly instead of wavy. 



