# Page:Popular Science Monthly Volume 81.djvu/376

will denote the presence of the ovary or the ♀ sex determiner. Then ${\displaystyle f}$ will denote the absence of femaleness and the absence of an ovary. Obviously a separate letter is not needed for this "anatomical factor," since the presence of an ovary is the objective criterion of the existence of the female sex, its absence of the existence of the male sex.
2. The "first production" factor. This is the primary physiological factor which in coexistence with ${\displaystyle F}$ makes the bird lay eggs during the winter period. Quantitatively it may be taken as determining a winter production of more than zero eggs and less than 30. The presence of this factor will be denoted by ${\displaystyle L_{1}}$.
3. The "second production" factor. This is a second physiological factor, which in coexistence with ${\displaystyle F}$ and ${\displaystyle L_{1}}$ leads to high fecundity. The presence of this factor will be denoted by ${\displaystyle L_{2}}$ and its absence by the corresponding small letter. When ${\displaystyle F}$ and ${\displaystyle L_{1}}$ are present the addition of ${\displaystyle L_{2}}$ makes a winter production of over 30 eggs. If ${\displaystyle F}$ is present and ${\displaystyle L_{1}}$ absent the presence of ${\displaystyle L_{2}}$ leads to a winter production of under 30 eggs. Thus either ${\displaystyle L_{1}}$ or ${\displaystyle L_{2}}$ alone makes a record of 30 eggs. They are independent determiners of this degree of production. It should be pointed out, however, that in spite of their equivalence in this regard the factors ${\displaystyle L_{1}}$ and ${\displaystyle L_{2}}$ are not qualitatively the same. That is, the increased production when ${\displaystyle L_{1}}$ and ${\displaystyle L_{2}}$ are both present is not because there are present two "doses" of the same determiner. The proof of this is found in the fact that when there are two "doses" of ${\displaystyle L_{1}}$ present in a bird it does not make her a high producer. ${\displaystyle L_{2}}$ may be considered an excess production factor, which erects a superstructure on the foundation furnished by ${\displaystyle L_{1}}$. In the absence of ${\displaystyle L_{1}}$ it lacks the foundation from which to start, and hence only can build about as high as ${\displaystyle L_{1}}$ would alone. Of course, it will be understood that in the presence of ${\displaystyle f}$ (absence of female sex and ovary) these physiological fecundity factors ${\displaystyle L_{1}}$ and ${\displaystyle L_{2}}$ are simply latent.
Using the letters in the manner defined above, and with the usual Mendelian method of writing gametic and zygotic formulæ, the data indicate that there exist 9 different types (in respect to fecundity) of Barred Plymouth Rock males, 6 types of Barred Plymouth Bock females, 3 types of Cornish Indian Game males, and 3 types of Cornish Indian Game females. The only point needing particular attention in reference to these formulas is that the factor ${\displaystyle L_{2}}$, the excess production factor, behaves in inheritance as a sex-limited or sex-correlated character. It is repelled by the female determiner ${\displaystyle F}$. It is thus like the barred pattern factor in the Barred Plymouth Rock fowl.[1] 3 In consequence gametes of the type ${\displaystyle FL_{2}}$ are never formed. Any gamete which bears ${\displaystyle F}$ does not, under any circumstance, ever carry ${\displaystyle L_{2}}$. All females