Morphological Variability in Embryogenesis of the Domestic Fowl and Factors Affecting It

Flock variability of the morphological development of the embryos during the whole embryogenetic period is determined by individual variability (the variation of this character in the embryos from the same female). A similarity of manifestation of this variability is evidently due to the duration of the period during which the eggs remain in the hen genital tract, and is, therefore, of parotypical character. The relationship found is limited by the reproductive processes in embryogenesis. In post-embryogenesis the regularities of the development and growth of chickens change, and the variability curve becomes different. The effect of external factors on the differentiation rate of embryos (the duration of the photoperiod, to some extent, the age of birds and keeping conditions) appear to take form indirectly through changes in the period during which the eggs remain in the female body.