The rate of growth of the chick embryo depends upon an inherent growth rate, probably identical for all breeds. This rate is modified during incubation in direct proportion to a function of egg size. The increments in wet weight of the embryo are proportional to a function of the weight of the yolk sac, from the time of establishment of the circulation to the time of the changes preparatory to hatching. Both function and proportionality are probably identical for all breeds of chicken, regardless of egg size.

The growth in weight of the allantois and the yolk sac have been measured quantitatively for the first time. The weight of the allantois in eggs of different sizes is roughly proportional to the two-thirds power of egg weight after the first three or four days of its growth. During the initial period of its development the relative size is apparently independent of breed, egg size, or embryo weight. The yolk-sac weight in eggs of different sizes is roughly proportional to the circumference of the yolk after a similar initial period of independent growth.

Inclusion of the living material in the embryonic membranes in calculations of the rate of physiological processes of the embryo indicates that they are probably of the same order of magnitude throughout the incubation period rather than of sharply decreasing magnitude as supposed by some previous workers.

1

The term “standard” is used in this paper to designate the eggs of approximate standard size, average about 60 gm., not the exact standard weight, 56-6 gm.

1
Coefficient of deviation, designated as C. of D. in the graphs, is
in which W—observed value, Wo—calculated value, and N = number of observed values (cf. Titus and Hendricks, 1930, p. 289).
1

See Romanoff (1930) for detailed account of changes in hydration of the yolk.

1
The relative values were obtained by solving the equation
in which Y = yolk-sac weight on a given day of the incubation period for a given set of data; X = yolk-sac weight on a given day of the incubation period for the standard egg data; A = a parameter determined from the data by method of least squares.

This weights the later, heavier values, which was deemed proper because these values should show the limiting effects of yolk size more than the values during the first days of incubation. They would be less affected by slight temperature variations also.

1

These units were used to avoid negative logarithms and for no other reason.

Copyright © 1932 The Company of Biologists Ltd.
1932
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