<P> In the mid 16th century, Gabriele Falloppio (discoverer of the fallopian tubes), described what are now known as the lacteals as "coursing over the intestines full of yellow matter ." In about 1563 Bartolomeo Eustachi, a professor of anatomy, described the thoracic duct in horses as vena alba thoracis . The next breakthrough came when in 1622 a physician, Gaspare Aselli, identified lymphatic vessels of the intestines in dogs and termed them venae alba et lacteae, which is now known as simply the lacteals . The lacteals were termed the fourth kind of vessels (the other three being the artery, vein and nerve, which was then believed to be a type of vessel), and disproved Galen's assertion that chyle was carried by the veins . But, he still believed that the lacteals carried the chyle to the liver (as taught by Galen). He also identified the thoracic duct but failed to notice its connection with the lacteals . This connection was established by Jean Pecquet in 1651, who found a white fluid mixing with blood in a dog's heart . He suspected that fluid to be chyle as its flow increased when abdominal pressure was applied . He traced this fluid to the thoracic duct, which he then followed to a chyle - filled sac he called the chyli receptaculum, which is now known as the cisternae chyli; further investigations led him to find that lacteals' contents enter the venous system via the thoracic duct . Thus, it was proven convincingly that the lacteals did not terminate in the liver, thus disproving Galen's second idea: that the chyle flowed to the liver . Johann Veslingius drew the earliest sketches of the lacteals in humans in 1647 . </P> <P> The idea that blood recirculates through the body rather than being produced anew by the liver and the heart was first accepted as a result of works of William Harvey--a work he published in 1628 . In 1652, Olaus Rudbeck (1630--1702), a Swede, discovered certain transparent vessels in the liver that contained clear fluid (and not white), and thus named them hepatico - aqueous vessels . He also learned that they emptied into the thoracic duct, and that they had valves . He announced his findings in the court of Queen Christina of Sweden, but did not publish his findings for a year, and in the interim similar findings were published by Thomas Bartholin, who additionally published that such vessels are present everywhere in the body, not just in the liver . He is also the one to have named them "lymphatic vessels ." This had resulted in a bitter dispute between one of Bartholin's pupils, Martin Bogdan, and Rudbeck, whom he accused of plagiarism . </P> <P> Galen's ideas prevailed in medicine until the 17th century . It was thought that blood was produced by the liver from chyle contaminated with ailments by the intestine and stomach, to which various spirits were added by other organs, and that this blood was consumed by all the organs of the body . This theory required that the blood be consumed and produced many times over . Even in the 17th century, his ideas were defended by some physicians . </P> <P> Alexander Monro, of the University of Edinburgh Medical School, was the first to describe the function of the lymphatic system in detail . </P>

Classify the tissues and organs as being either primary or secondary lymphatic structures