AGE, GROWTH AND DEATH
209
Fig. 34.
This completes the series of curves which I had prepared to present to you to show the rate of growth in animals from their birth only, but of course there has been also a growth of the animals which preceded their birth, and that now must briefly be considered.
The mere inspection of developing embryos of known ages gives us some idea of the rate of growth. With the aid of the lantern I will ask you to look with me at some pictures of the developing chick and developing rabbit. Let us begin with the chick.[1]
- ↑ During the lectures a series of lantern slides-were projected upon the screen, made from photographs of mounted specimens of chicken embryos, which showed very clearly the progress of development in the chick during the very early stages. The first figure illustrated a chick of 18 hours' incubation. The embryo had been skimmed off from the surface of the egg, hardened, colored artificially and mounted in the manner of the ordinary microscopical preparation in Canada balsam. At this age the naked eye can just distinguish a line, which indicates the position of the axis of the embryo. The unaided eye can recognize nothing more. In the second picture the head and neck of the embryo were easily distinguishable, and a few of the earliest primitive segments. The third slide showed a stage of a day and a half. The spinal cord and brain were distinctly differentiated, and numerous so-called "blood islands" scattered about.
