Ex ovo omnia.
All out of the egg.

A hen is only an egg's way of making another egg.

A story about the Jack Spratts of medicine [was] told recently by Dr. Charles H. Best, co-discoverer of insulin. He had been invited to a conference of heart specialists in North America. On the eve of the meeting, out of respect for the fat-clogs-the-arteries theory, the delegates sat down to a special banquet served without fats. It was unpalatable but they all ate it as a duty. Next morning Best looked round the breakfast room and saw these same specialists—all in the 40-60 year old, coronary age group—happily tucking into eggs, bacon, buttered toast and coffee with cream.

Always preoccupied with his profound researches, the great Newton showed in the ordinary-affairs of life an absence of mind which has become proverbial. It is related that one day, wishing to find the number of seconds necessary for the boiling of an egg, he perceived, after waiting a minute, that he held the egg in his hand, and had placed his seconds watch (an instrument of great value on account of its mathematical precision) to boil!
This absence of mind reminds one of the mathematician Ampere, who one day, as he was going to his course of lectures, noticed a little pebble on the road; he picked it up, and examined with admiration the mottled veins. All at once the lecture which he ought to be attending to returned to his mind; he drew out his watch; perceiving that the hour approached, he hastily doubled his pace, carefully placed the pebble in his pocket, and threw his watch over the parapet of the Pont des Arts.

An egg is a chemical process, but it is not a mere chemical process. It is one that is going places—even when, in our world of chance and contingency, it ends up in an omelet and not in a chicken. Though it surely be a chemical process, we cannot understand it adequately without knowing the kind of chicken it has the power to become.

By its very nature the uterus is a field for growing the seeds, that is to say the ova, sown upon it. Here the eggs are fostered, and here the parts of the living [fetus], when they have further unfolded, become manifest and are made strong. Yet although it has been cast off by the mother and sown, the egg is weak and powerless and so requires the energy of the semen of the male to initiate growth. Hence in accordance with the laws of Nature, and like the other orders of living things, women produce eggs which, when received into the chamber of the uterus and fecundated by the semen of the male, unfold into a new life.

Do you see this egg? With this you can topple every theological theory, every church or temple in the world.

Every bird which flies has the thread of the infinite in its claw. Germination includes the hatching of a meteor and the tap of a swallow's bill breaking the egg, and it leads forward the birth of an earth-worm and the advent of Socrates.

Every complete set of chromosomes contains the full code; so there are, as a rule, two copies of the latter in the fertilized egg cell, which forms the earliest stage of the future individual. In calling the structure of the chromosome fibres a code-script we mean that the all-penetrating mind, once conceived by Laplace, to which every causal connection lay immediately open, could tell from their structure whether the egg would develop, under suitable conditions, into a black cock or into a speckled hen, into a fly or a maize plant, a rhododendron, a beetle, a mouse or a woman. To which we may add, that the appearances of the egg cells are very often remarkably similar; and even when they are not, as in the case of the comparatively gigantic eggs of birds and reptiles, the difference is not so much in the relevant structures as in the nutritive material which in these cases is added for obvious reasons.
But the term code-script is, of course, too narrow. The chromosome structures are at the same time instrumental in bringing about the development they foreshadow. They are law-code and executive power?or, to use another simile, they are architect's plan and builder's craft-in one.

Everyone admits that the male is the primary efficient cause in generation, as being that in whom the species or form resides, and they further assert that his genitures emitted in coitus causes the egg both to exist and to be fertile. But how the semen of the cock produces the chick from the egg, neither the philosophers nor the physicians of yesterday or today have satisfactorily explained, or solved the problem formulated by Aristotle.

In systemic searches for embryonic lethal mutants of Drosophila melanogaster we have identified 15 loci which when mutated alter the segmental patterns of the larva. These loci probably represent the majority of such genes in Drosophila. The phenotypes of the mutant embryos indicate that the process of segmentation involves at least three levels of spatial organization: the entire egg as developmental unit, a repeat unit with the length of two segments, and the individual segment.
[Co-author with American physiologist Eric Wieshaus (1947-)]

It is therefore proper to acknowledge that the first filaments of the chick preexist in the egg and have a deeper origin, exactly as [the embryo] in the eggs of plants.

Let us now recapitulate all that has been said, and let us conclude that by hermetically sealing the vials, one is not always sure to prevent the birth of the animals in the infusions, boiled or done at room temperature, if the air inside has not felt the ravages of fire. If, on the contrary, this air has been powerfully heated, it will never allow the animals to be born, unless new air penetrates from outside into the vials. This means that it is indispensable for the production of the animals that they be provided with air which has not felt the action of fire. And as it would not be easy to prove that there were no tiny eggs disseminated and floating in the volume of air that the vials contain, it seems to me that suspicion regarding these eggs continues, and that trial by fire has not entirely done away with fears of their existence in the infusions. The partisans of the theory of ovaries will always have these fears and will not easily suffer anyone's undertaking to demolish them.

Monotremes oviparous, ovum meroblastic.
The platypus and the echidna lay eggs which, having considerable yolk, lead to the development of the embryo above the yolkmass.

On entering his [John James Audubon] room, I was astonished and delighted to find that it was turned into a museum. The walls were festooned with all kinds of birds’ eggs, carefully blown out and strung on a thread. The chimney-piece was covered with stuffed squirrels, raccoons, and opossums; and the shelves around were likewise crowded with specimens, among which were fishes, frogs, snakes, lizards, and other reptiles. Besides these stuffed varieties, many paintings were arrayed on the walls, chiefly of birds.

The development of an organism … may be considered as the execution of a 'developmental program' present in the fertilized egg. … A central task of developmental biology is to discover the underlying algorithm from the course of development.

The fibrous material and muscle were thus digested in the same way as the coagulated egg albumen, namely, by free acid in combination with another substance active in very small amounts. Since the latter really carries on the digestion of the most important animal nutrient materials, one might with justice apply to it the name pepsin.

The serum, when subjected to heat, coagulates and hardens like egg. This property is one of its striking characteristics; it is attributed to a particular substance which is thereby readily recognizable, and which is called albumine, because it is the one present in egg white, termed albumen.

There is no generation from an egg in the Mineral Kingdom. Hence no vascular circulation of the humours as in the remaining Natural Kingdoms.

This, however, seems to be certain: the ichor, that is, the material I have mentioned that finally becomes red, exists before the heart begins to beat, but the heart exists and even beats before the blood reddens.

We [may] answer the question: “Why is snow white?” by saying, “For the same reason that soap-suds or whipped eggs are white”—in other words, instead of giving the reason for a fact, we give another example of the same fact. This offering a similar instance, instead of a reason, has often been criticised as one of the forms of logical depravity in men. But manifestly it is not a perverse act of thought, but only an incomplete one. Furnishing parallel cases is the necessary first step towards abstracting the reason imbedded in them all.

With the tools and the knowledge, I could turn a developing snail's egg into an elephant. It is not so much a matter of chemicals because snails and elephants do not differ that much; it is a matter of timing the action of genes.

[An] old Pythagorean prejudice … thought it a crime to eat eggs; because an egg was a microcosm, or universe in little; the shell being the earth; the white, water; fire, the yolk; and the air found between the shell and the white.