Observations on the changes the egg undergoes during incubation in the common fowl, illustrated by microscopical drawings

Abstract

The molecule from which the future embryo is to be formed, is observed upon the surface of the yolk before it leaves the ovarium. It consists of globules 1/1800th of an inch in diameter, surrounded by a mixture of these and larger oval globules, similar to those of the bird’s blood, excepting their red colour; some oil is also discover­able. In the passage of the yolk along the oviduct, it acquires the albumen and its membrane; in this passage also the thread-like sub­stances, which Mr. Hunter called the poles, were formed. Sir Everard next describes the changes which the egg undergoes during incu­bation. In four hours the rudiments of the embryo are perceptible; and in eight hours the brain and spinal marrow are surrounded by an amnion, all of which increase in distinctness for the first twenty-four hours. In thirty-six hours the intervertebral nerves and the lobular structure of the brain, and in forty-four hours the eye and heart are seen, and in two days and twelve hours it contained red blood, and ar­terial ramifications began to be formed. In three days the rudiments of the wings and legs were formed. These parts progressively in­crease until the sixth day, when the amnion is filled with water, and shortly afterwards the parietes of the thorax begin to form, and mus­cular action becomes evident. In seven days and twelve hours arterial pulsation was first perceived; and in eight days and twelve hours the liver was seen. In ten days and twelve hours the cutis was covered with cuticle, and the gizzard and intestinal canal were formed. The above, as well as several intermediate changes, are illustrated by drawings, and the author concludes the paper with some observations upon the circumstances in which the changes observed during the in­cubation of the egg, differ from those which occur in the ovum of the quadruped.