_Born in Delft, Holland, October 24, 1632, Anthony Van Leeuwenhoeck, a lens-maker for microscopes, made several important biological discoveries. In 1673 he noticed the red globules in the blood; in 1675 he discovered animalculæ in water; in 1677 he described the spermatozoa; in 1690 he traced the passage of blood from the arteries into the veins. Among his other achievements were his investigations of the tubules of teeth, the solidity of hair, the structure of the epidermis, and his descriptions of insect anatomies. He announced most of his findings to the Royal Society of London. Against the generally accepted idea of spontaneous generation, he held that all things generated their kind. He died at Delft, August 26, 1723._ OBSERVATIONS ON ANIMALCULÆ[10] In the year 1675, I discovered very small living creatures in rain water, which had stood but few days in a new earthen pot glazed blue within. This invited me to view this water with great attention, especially those little animals appearing to me ten thousand times less than those represented by M. Swammerdam, and by him called water-fleas, or water-lice, which may be perceived in the water with the naked eye. The first sort I several times observed to consist of 5, 6, 7, or 8 clear globules without being able to discern any film that held them together, or contained them. When these animalcula or living atoms moved, they put forth two little horns, continually moving. The space between these two horns was flat, though the rest of the body was roundish, sharpening a little towards the end, where they had a tail, near four times the length of the whole body, of the thickness, by my microscope, of a spider’s web; at the end of which appeared a globule of the size of one of those which made up the body. These little creatures, if they chanced to light on the least filament or string, or other particle, were entangled therein, extending their body in a long round, and endeavoring to disentangle their tail. Their motion of extension and contraction continued a while; and I have seen several thousands of these poor little creatures, within the space of a grain of gross sand, lie fast clustered together in a few filaments.