Mon. Giron[17] expresses the opinion that the relative age and vigor of the parents exercises very considerable influence, and states as the results of his observation, that the offspring of an old male and a young female resembles the father less than the mother in proportion as the mother is more vigorous and the father more decrepit, and that the reverse occurs with the offspring of an old female and a young male.
Among the more recent theories or hypotheses which have been started regarding the relative influence of the male and female parents, those of Mr. Orton, presented in a paper read before the Farmers' Club at Newcastle upon Tyne, on the Physiology of Breeding, and of Mr. Walker in his work on Intermarriage, as they both arrived to a certain extent, at substantially the same conclusions by independent observations of their own and as these seem to agree most nearly with the majority of observed facts, are deemed worthy of favorable mention.
The conclusions of Mr. Orton, briefly stated,[18] are, that in the progeny there is no casual or haphazard blending of the parts or qualities of the two parents, but rather that organization is transmitted by halves, or that each parent contributes to the formation of certain structures, and to the development of certain qualities. Advancing a step further, he maintains, that the male parent chiefly determines the external characters, the general appearance, in fact, the outward structure and locomotive powers of the offspring, as the framework, or bones and muscles, more particularly those of the limbs, the organs of sense and skin; while the female parent chiefly determines the internal structures and the general quality, mainly furnishing the vital organs, i.e., the heart, lungs, glands and digestive organs, and giving tone and character to the vital functions of secretion, nutrition and growth. "Not however that the male is without influence on the internal organs and vital functions, or the female without influence on the external organs and locomotive powers of their offspring. The law holds only within certain restrictions, and these form as it were a secondary law, one of limitations, and scarcely less important to be understood than the fundamental law itself."