subsequently, and assisted him when in Amsterdam in after years, by obtaining permission for him to dissect human bodies. His fellow-pupil was Nicholas Steno, of whom more will be said under the title of “Heroes of Geology.” On his return to Leyden, Swammerdam discovered the method of injecting arteries with coloured wax, and of keeping the internal organs in a dry condition for purposes of study, and investigated the nature of the lymphatics. He graduated soon after, and after receiving his diploma, returned to his old love, nature, and occupied nearly all his time in the anatomy and physiology of insects. Swammerdam worked so incessantly, that he got into bad health, and was obliged to relinquish the medical profession for a time. He followed up his researches into the minute construction of insects, and really never ceased them until death. The Grand Duke of Tuscany visited Amsterdam at this time, and examined Swammerdam’s collections. Greatly impressed with their value, and with the splendid dissections, he offered a home to the young naturalist in his palace, and twelve thousand florins for the collection. Swammerdam, however, did not care to wear a collar; and loving freedom of thought, which he did not think he would have in Italy, declined the offer. He knew that he would be expected to change his religious tenets, and said that he would not sell his soul for money. He published a “General History of Insects,” in 1669, and soon afterwards broke down, entirely, in health, so that he had to go into the country to rest and do nothing. But this was impossible; and he began to study bees, and their natural history. Probably it was this constant weak health, and the solitude necessary for the peculiar nature of his work and observations, that had a very remarkable influence on the mind and emotions of this great investigator. Always religious, he longed more and more for communion with his Maker and the author of all the wonders he was constantly studying. When in better health he was happy in his thoughts, and considered that it was his duty to study nature; but when ill, from the effects of overwork, he began to think that his labours were leading him astray, and that to seek the good opinion of his fellow-creatures and to become famous, was a sin. Sometimes he gave up science, to begin again with fresh zeal, and then he would neglect it, giving up his whole time to religion. Unfortunately he was unreasonable in his method of working. Boerhaave, the great physician, thus wrote of Swammerdam: “He laboured so assiduously at this work as to destroy his constitution, nor did he ever recover a shadow of his former strength. The labour, in fact, was beyond the power of ordinary men—all day he was employed in examining objects, and at night described and delineated what he had seen by day. At six in the morning, in summer, he began to receive sufficient light from the sun to enable him to trace the objects of his examination.