EXERCISE THE NINETEENTH.
The fifth inspection of the egg.
On the sixth day the three cells of the head present them- selves more distinctly, and the coats of the eyes are now ap- parent ; the legs and the wings also bud forth, much in the way in which, towards the end of June, we see tadpoles getting their extremities, when they quit the water, and losing their tails assume the form of frogs.
In the chick, the rump has still no other form than is con- spicuous in animals at large, even in serpents ; it is a round and slender tail. The substance of the heart now grows upon the pulsating vesicle ; and shortly afterwards the rudiments of the liver and lungs are distinguished; the bill, too, makes its ap- pearance at the same time. Everything is of a pure white co- lour, especially the bill. About the same epoch all the viscera and the intestines are conspicuous. But the heart takes precedence of all the parts ; and the lungs are visible before the liver or brain. The eyes, however, are seen first of all, by reason of their large size and black colour.
And now, too, the embryo has a power of motion, and raises its head and slightly twists itself, although there is still nothing of the brain to be seen, but only a little limpid fluid inclosed in a vesicle. It is at length a perfect maggot, only differing from a caterpillar in this, that when worms are set free from their cells they creep about hither and thither and seek their food, whilst the worm in the egg is stationary, and, surrounded with its proper food, is furnished with aliment through the umbilicus.
The viscera and intestines being now formed, and the foetus able to execute motions, the anterior portion of the body, with- out either thorax or abdomen, is perceived to be completely open ; so that the heart itself, the liver and the intestines, are seen to hang pendulous externally.
Towards the end of this day and the beginning of the seventh, the toes are distinguished, and the embryo already presents the outlines of the chick, and opens its beak, and kicks with its
