At _ten weeks_ the embryo is from one and a half to two and a half inches long, and its weight is from one ounce to an ounce and a half, the eyelids are more developed and descend in front of the eyes; the mouth begins to be closed by the development of the lips. The walls of the chest are more completely formed, so that it is no longer possible to see the movements of the heart. The fingers become distinct and the toes appear as small projections webbed together like a frog's foot. At about this period the sexual organs show their development as follows: On each side of the urinary locality an oblong fold becomes distinguishable; in course of progress if these folds remain separate, a little tubercle forms in the anterior commissure which becomes the clitoris; the nymphae develop, the urethra forms between them, and the female sex is determined. If, on the other hand, these folds unite into a rounded projection the scrotum is formed, the little tubercle above becomes the penis and hence the male sex. The testicles forming within the body, descend later into the scrotum, and organs similar to them, their counterparts, form in the female and are called ovaries. These ovaries are found attached to an organ called the womb, and this again is united with the vagina, which leads downwards and outwards between the labia majora.[B] [B] For fuller particulars see Guernsey's Obstetrics. At the end of the _third month_ the weight of the embryo is from three to four ounces and its length from four to five inches, the eyeballs are seen through the lids, the pupils of the eyes are discernible, the forehead, nose and lips can be clearly distinguished. The finger nails resemble thin membranous plates, the skin shows more firmness, but is still rosy-hued, thin and transparent. The sex can now be fully determined. At the end of the _fourth month_ the product of conception is no longer called an embryo, but a foetus. The body is from six to eight inches in length and weighs six or seven ounces. A few little white hairs are seen scattered over the scalp. The development of the face is still imperfect. The eyes are now closed by their lids, the nostrils are well-formed, the mouth is shut in by the lips and the sex is still more sharply defined. The tongue may be observed far back in the mouth, and the lower part of the face is rounded off by what a little later will be a well-formed chin. The movements of the foetus are by this time plainly felt by the mother, and if born at this time it may live several months.