Antonii a Leeuwenhoek ... Epistolae physiologicae super compluribus naturae arcanis

LETTER XIX. Page 170

ON the veins of pears, by means of which pears grow to their proper size. There is no circulation of fluids in fruits. The countless branches of those small veins. How perfect the structure of the seed, which is contained within the capsule or follicle of the pear. In such a seed, both the small vessels and the valves of the vessels were discovered by the Author. The function and use of those valves. A double species of vessels and valves. Other annotations concerning the pear. The plant of the tree itself is seen within the seed. The seeds grow through certain, as it were, cords or twisted threads. The aforementioned plantlet is teeming with most abundant vessels. Concerning the coconut original: "Nuce Cocco". Its filaments are truly vessels, etc. The pear, to the extent that it exists, is composed almost entirely of vessels and membranes: which vessels sit in great number upon the outermost skin of the pear. What use that skin serves. Concerning the spiral parts of the tendons and fibrils. A membrane not passable through any cavity. No blood is poured into the fibrils through the extremities of the arteries.

LETTER XX. Page 183

A succinct response to certain petty arguments against the seminal animalcules original: "Animalcula seminalia". For what reason twins are so rare in certain animals. Whence it comes to pass that among so many myriads of seminal animalcules, one grows rather than others. The animalcules, in the masculine seed of quadrupeds and fish, scarcely differ in size from one another. The eggs are equally large in yearling fish as they are in adult and aged fish. Yearling fish, in the same species, do not produce smaller offspring than the largest fish. Larger and voracious fish produce only a single offspring. A description of the tendons. Individual fibrils, from which a tendon is composed, are a hundred times thinner than a hair. No air in the arteries, veins, tendons, or membranes. The motion of the heart is explained.