Page:Popular Science Monthly Volume 81.djvu/371

Rh During the course of this investigation into the inheritance of fecundity in the domestic fowl, which has now involved thirteen generations and several thousand individuals, two definite and clear-cut results have come to light. These are:

First: that the record of egg production or fecundity of a hen is not, of itself, a criterion of any value whatsoever from which to predict the probable egg production of her female progeny. An analysis of the records of production of large numbers of birds shows beyond any possibility of doubt that, in general, there is no correlation between the egg production of individuals and either their ancestors or their progeny.

Second: that, notwithstanding the fact just mentioned, fecundity is, in some manner or other, inherited in the domestic fowl. This must clearly be so, to mention but a single reason, because it has been possible to isolate and propagate from a mixed flock "pedigree lines" or strains of birds which breed true, generation after generation, to definite degrees of fecundity. Some of these lines breed true to a high condition or degree of the character fecundity; others to a low state or degree.

Definite as these results are, they give no clue as to how fecundity is inherited; what the mechanism is. It is believed that now a first approximation to the solution of this problem has finally been reached. While there remain obscure points yet to be cleared up, and more data are needed definitely to decide between certain alternatives, yet the results now in hand appear to indicate quite clearly the general character of the mechanism of the inheritance of fecundity, and to show what lines further investigation of the problem may most profitably take.

At the outstart it will be well to understand clearly what is meant by the term fecundity as here used. I have used the term "fecundity" only to designate the innate potential reproductive capacity of the individual organism, as denoted by its ability to form and separate from the body mature germ cells. Fecundity in the female will depend upon the production of ova and in the male upon the production of spermatozoa.

Fecundity is obviously a character depending upon the interaction of several factors. In the first place the number of ova separated from the body by a hen or any other animal must depend, in part at least, upon an anatomical basis, namely the number of ova present in the ovary and available for discharge. Further there must be involved a series of physiological factors. It has been possible to prove that the mere presence of an anatomically normal reproductive system, including a normal ovary with a full complement of ova, and a normal