Antonie van Leeuwenhoek

I've never taught one, because if I taught one, I'd have to teach others... I would give myself over to a slavery, whereas I want to stay a free man.

In rain water, I observed a small red worm and two other kinds of very minute insects; of those of the larger size, I judged that 30,000 together would not equal a coarse sand.

My determination is not to remain stubbornly with my ideas, but I'll leave them and go over to others as soon as I am shown plausible reasons which I can grasp.

I now found that the spider cannot fix its thread to anything without imprinting the hind part of its body on the place, by which pressure it emits an incredible number of excessively small threads diverging in every direction from whence we may conclude that as soon as the threads are exposed to the air, they lose their viscosity or gluey quality.

I have lately examined water, in which beaten pepper was steeped, and found two sorts of animals for shape, and each of those sorts to contain greater and smaller kinds: the greater I supposed the elder, the less the younger.

If we now plainly perceive that the passage of the blood from the arteries into the veins of the tadpole is not performed in any other than those vessels, which are so minute as only to admit the passage of a single globule at a time, we may conclude that the same is performed in like manner in our own bodies and in those of other animals.

Whenever I found out anything remarkable, I have thought it my duty to put down my discovery on paper, so that all ingenious people might be informed thereof.

In treating of the oak, I have considered that the species of it growing in warm climates is superior to that which is produced in cold countries. But we must not imagine this to be the case with all woods; on the contrary, the fir timber grown in cold countries is superior to that produced in warm ones, where its growth is rapid.

I must confess... I don't know any tongue but the Nether-Dutch.

Man comes not from an egg but from an animalcule that is found in male sperm.

How inscrutable and incomprehensible are the hidden works of Nature!

How little do we discover in comparison of those things which now are and forever will be hidden from our sight? The whole of which I am fully persuaded no one will ever be able to dive into, and to explain their causes and effects.

Life lives on life - it is cruel, but it is God's will. And it is for our good, of course, because if there weren't little animals to eat up the young mussels, our canals would be choked by those shellfish, for each mother has more than a thousand young ones at a time!

No one can pretend to say that a fish is ever killed by heat, for many kinds of fish, in the middle of summer, and in the burning heat of the sun, do either play, as it were, on the surface of the water, or hide themselves under the leaves, weeds, or other substances at the bottom.

We will admit that, out of the mud or sand which is found on the seashore or the beds of our rivers, at low water, shellfish or testaceous animals come forth, but it does not from thence by any means follow that they are produced without any regular course of generation.

I have oft-times been besought, by divers gentlemen, to set down on paper what I have beheld through my newly invented microscopia, but I have generally declined.

People who look for the first time through a microscope say, 'Now I see this, and then I see that,' and even a skilled observer can be fooled. On these observations I have spent more time than many will believe, but I have done them with joy, and I have taken no notice of those who have said, 'Why take so much trouble,' and, 'What good is it?'

For my part, I hold it equally impossible for a small shellfish to be produced without generation as for a whale to have its origin from the mud.

If any person examines by the microscope that part towards the extremity of the spider's body from whence its thread proceeds, he will observe the spot to be, as it were, surrounded by five several protuberances or risings, each ending in a point and altogether forming a kind of enclosure.

For my part, I would say that the male sperm and seeds of plants have been penetrated so far that there is nothing further to discover in this great secret, but I could err in my opinion.