Malpighi, a naturalist in Bologna who also served as a Vatican physician, established the microscope as an essential research tool in the study of anatomy, whether plant, animal or human.  

Malpighi published remarkably detailed drawings showing the development of a chick embryo inside an egg. With each image, the embryo increasingly resembles the chick that will hatch after 21 days of incubation.  Later illustrations show the umbilical cord and egg sac.  Malpighi wrote, “I perceived the enclosed fetus, whose head clearly appeared.  For the thin and clear texture of the amniotic fluid was frequently transparent, so that the enclosed animal came into view.” Although Malpighi reported that he had never observed similar forms in unfertilized eggs, 18th century “ovists” (advocates of the view that the young are preformed in the egg) cited his study of the chick embryo as a leading piece of evidential support.

In other works, Malpighi described tiny tubules in the anatomy of silkworms and noted similar tubules in the microscopic structures of plants.  Working mainly with frogs but extrapolating to humans, he was able to observe red blood cells, and the tiny capillaries connecting the smallest arteries and veins, as predicted by William Harvey.  He showed how the lungs allow the proximity of air and blood without their intermingling. Microscopic structures he discovered in the kidney and spleen remain named after him today.