In 1638, a goldsmith, Steno by name, living at Copenhagen, who was a tradesman of the King Christian IV. of Denmark, had a son. The young Nicholas was brought up carefully, evidently was well educated, and was destined for the medical profession. A strict Lutheran, he naturally went to Holland for a part of his education, and studied at Leyden under the very distinguished anatomists there, after he had taken his degree. Nothing is known about his person or habits, but the results of his constant labour prove him to have been a most industrious student, and also an investigator of the human frame in his early days of manhood. At first the medical profession was everything to him, and he studied human anatomy and physiology with great success, making some important and interesting discoveries. He discovered the duct or channel by which the saliva runs into the mouth from the salivary gland beneath the skin on the cheek, and in 1664 he published some researches on the manner in which the chick is nourished in the egg. Moreover, he examined the structures of the eye of the calf, the nature of the mucous secretion, and wrote on the heart. While engaged in these researches at Amsterdam, he heard of the death of his mother, and returned to Copenhagen. After a short stay there, he set out for Italy, taking France on his way; and he began a series of researches on the structure of the brain at Paris in 1664. Here a great change occurred, which influenced his future life in a remarkable degree. Steno, well known then as a successful investigator, came under the notice of a great French geographer, Thévenot, and, what was more important, became the friend of Bossuet, one of the greatest preachers and teachers the Roman Catholic Church has ever produced. Steno was so influenced by Bossuet, that he became converted to the Roman Catholic faith, and left the Lutheran Church. Going subsequently into Italy, Steno pursued his studies, and settled in Florence, in 1667, being well received by the Grand Duke Ferdinand II. de Medici. In spite of the somewhat natural jealousy of the medical men of the city, Steno was appointed physician to the Grand Duke, and prosecuted his anatomical studies under his influence. Then he came across a subject which directed his attention to geology, or rather to that part of the science which relates to extinct animals. In a letter to Thévenot, Steno describes the dissection of a shark which had been captured off Leghorn in 1666, and especially discussed the mode of growth of the teeth of the animal. At this time many fossils were picked up and gathered out of layers or strata, which were called by many curious names, and believed to be anything but what they really were. They were distinguished by Steno at once as shark’s teeth, and he insisted that sharks lived during the former ages of the globe, and that they had become entombed in the deposits which were then forming a stratum or layer of earth, the result