On Embryology

I. Embryology is a rather recent science.¹

¹ Cf. Miller, Embryology, 4th ed., New York, 1921.

In the year 1600 Fabricius ab Aquapendente wrote the book On the Formed Fetus, and four years later another, On the Formation of the Fetus.

In 1651 Harvey established the principle: Every living thing is from a living thing; but he thought that the egg was formed in the wall of the uterus under the action of the sperm. He wrote the work Exercises on the Generation of Animals, in which he describes an embryo of two days' incubation.

In 1672 Regnier de Graaf discovered eggs in mammals, as he says, or rather the vesicles containing them. Hence he sets forth the principle, Every living thing is from an egg, in the book On the Organs of Women Serving Generation.

Van Leeuwenhoek (or perhaps his disciple L. Hamm) discovered nemasperms in 1677: the male semen is not a mere fluid, but contains mobile filaments.

Cangiamila published in 1745 in Italian, and in 1758 in Latin and more extensively, the celebrated work Sacred Embryology; in 1755 Wolff wrote On the Theory of Generation.

In 1827 von Baer discovered the human ovule, and in the work On the Egg in the Genesis of Animals and Man he describes the egg, the yolk, and the vitelline membrane. Semen consists, as it were, of little animals, which after the manner of animals consist of a head and tail and move themselves; these he calls zoosperms or spermatozoa.

Prévost and Dumas, in 1824, demonstrated the intervention of nemasperms in fertilization. About the same time the germinal vesicle was discovered by Coste and Purkinje (1834), and the germinal spot by Wagner (1836).

From the year 1840, several men, such as Pander, Kolliker, and Reichert, applied the cellular theory. Kolliker himself and Virchow (in the year 1855) established the principle: Every cell is from a cell, every nucleus from a nucleus. In 1841 Kolliker discovered the origin of zoosperms, namely, from the transformation of the testicular cell, but thought them to be incomplete cells; in 1865 Schweigger and Le Valette asserted them to be complete cells.

In 1843 Barry discovered sperm in the ovule, not acting at a distance, as de Graaf had thought; in 1879 Fol detected its penetration into the ovule; in 1861 Gegenbaur showed the ovule to be a true cell.

Thus all the elements essential to the forming of the fetus are now scientifically known.

Now embryology investigates the formation of the embryo and all the phases which the fetus passes through in its development up to perfect birth.

II. The moral and pastoral questions concerning embryology pertain per se to the matter of justice, and sometimes per accidens to the matter of chastity: per se, namely, to the fifth precept of the Decalogue; per accidens, for example, when an operation is performed to impede conception or generation, also to the sixth.

But that these questions may be understood, it is necessary to possess sufficient notions of physiological science concerning the manner in which the fetus is formed and developed in the maternal uterus, lives there, and is born from it. These we set forth briefly in the little work Questions on Embryology and the Ministration of Baptism, I, q. 1.

For the solution of the questions, however, it is necessary to have recourse to certain theological principles, which we recalled to mind in the said little work, I, q. 2.

Some operations and incisions are performed during pregnancy or childbirth, and properly and immediately regard embryology itself; others are performed at an earlier time to impede pregnancy and childbirth, and these can be called by the one name sterilizations. Hence we shall speak:

I. On operations during pregnancy or childbirth, especially:

1. On Caesarean section and other incisions which injure the mother;
2. On embryotomy, or on incisions which injure the fetus;
3. On the procuring of abortion, which acts upon the mother and the fetus at the same time;
4. On operations concerning ectopic fetuses.

II. On sterilization, especially:

1. On the morality of private sterilization;
2. On the morality of sterilization to be imposed by public authority;
3. On cooperation in sterilization.

To these will be added an appendix on the marriage of sterilized persons.