_At the twelfth day_ the ovum is about the size of a large pea, it is composed of a vesicle containing a thick fluid, called the _germ_, which corresponds to the opaque substance seen in the white of a fecundated bird's egg, and of a yellowish substance, in which it floats, called the _vitellus_, which answers to the yelk. The whole being surrounded by two membranous coverings, the outer one called the _chorion_, and the inner one the _amnion_. Between these is a gelatinous substance, and within the amnion is a fluid, called the liquor amnii. The two membranes, the liquor amnii, and the inclosed ovum, are called the _ovulum_! Immediately after conception the uterus begins to secrete, from its inner walls, another membrane, very delicate, called the _decidua_. This lines the whole cavity, so that when the ovulum passes out of the tube it is met by this lining which seems to prevent its entrance into the womb. The ovulum, however, presses upon it and so makes a depression, like a nest, in which it lies. This prevents its moving about, or falling to the bottom of the womb. The weight of the entire ovulum is about one grain. The embryo commences in the germ, and may now be seen about the size of a pin's point. The vitellus removes away from it, but remains connected by a small pedicel or thread-like tube, down which it is gradually absorbed as nutriment. A small white thread, scarcely perceptible, may be seen sometimes as early as this period, being the commencement of the brain and spinal marrow. The mouth is visible also from the twelfth to the twentieth day, and frequently the eyes. These are placed at first on the side of the head, like those of quadrupeds, and move round to the front afterwards. _At twenty-five days_, the embryo is about the size of a large ant, which it also resembles in form. It begins to have a little more consistence, and the future bones begin to resemble cartilage, or gristle. A small groove may be seen denoting the neck, which thus indicates the separation of the head from the trunk. The weight is three or four grains. _The first month_, it is about the size of a Bee, and is somewhat like a small worm bent together. The arms may be seen like two little warts. They are first formed under the skin, and shoot out like buds, growing straight from the body; afterwards they become folded together, in a curious manner, upon the breast. The head is as large as the rest of the body, and upon it we can now see distinctly the eyes, like two black dots, the mouth, like a line, and also the nose. The lower extremity is lengthened out like a tail. Weight about ten grains.