The following points highlight the eleven eminent zoologists of all times. The eminent zoologists are: 1. W. Harvey (1578-1657) 2. C. Linnaeus (1707-1778) 4. M. J. Schleiden (1804-1881) 5. J. B. Lamarck (1774-1829) 6. C. Darwin (1809-1882) 7. H. de Vries (1848-1935) 8. G. Mendel (1822-1884) 9. L. Pasteur (1822-1895) 10. H. Spemann (1860-1941) 11. T. H. Morgan (1866-1945).
Eminent Zoologist # 1. W. Harvey (1578-1657):
William Harvey was born in a wealthy family in Folkstone, England. He had his schooling in the King’s School at Canterbury and at the age of sixteen entered Cain’s College. Here he studied Latin and Greek to become a graduate with arts degree.
In 1598 he came to University of Padua, Italy, and studied Anatomy and Physiology from Fabricius. Fabricius was the most learned and honoured teacher in Italy at that time. He came back to England in 1602 and obtained M.D. degree from Cambridge. In 1615 he became lecturer of anatomy in the Royal College of Physicians in London.
Harvey’s book “Anatomical dissertation concerning the motion of the heart and blood” is still considered as one of the greatest monuments in Biology. He was the first amongst the biologists who gave a really reasonable explanation, in physical terms, of any bodily process.
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His investigation on the anatomy of about sixty animals and embryology of insects and vertebrates had a tremendous influence in promoting further biological research.
Eminent Zoologist # 2. C. Linnaeus (1707-1778):
Caroleus von Linnaeus, son of a poor Swedish clergyman, was an eminent naturalist. He was a student of medicine in Upsala. In 1732 the Royal Society of Upsala sent him to Lapland as a collector and observer. On returning he completed his studies in medicine from the University of Hardewyk in 1735. Within a short time he was appointed as Professor of Natural History of Upsala.
Linnaeus had a fascination to classify animals and plants. He introduced the system of classification which is known as Binomial nomenclature and placed all the known plants and animals in his classificatory system. He classified not only plants and animals but also the minerals and even diseases.
His great contributions were the publications of Systema Naturae (1735), Foundamenta Botanica (1735), Bibliotheca Botanica (1735) and Genera Plantarum (1737). The Systema Naturae is not only a treatise but also a catalogue of the production of nature, most methodically arranged. His binomial nomenclature system is still in practice all over the world.
Eminent Zoologist # 3. M. J. Schleiden (1804-1881):
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Schleiden, a German botanist, was a graduate in medicine but his studies centred mainly around Botany. The nucleus in the plant cells was discovered by Robert Brown in 1831 and this greatly influenced the studies of Schleiden. In 1838, he suggested that the cells were the structural units of plants. His co- worked Theodor Schwann concluded that Schleiden’s idea is applicable to animals also.
The cell theory, though really postulated by Schwann, is based on Schleiden’s observations also. The cell theory has played a very important role in the understanding of structures and functions of different organs of the living organism.
The present-day modification of the cell theory of Schleiden and Schwann stands as:
1. Cells are the structural and functional units of the body of an organism.
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2. Every individual begins its life from a single cell.
3. New cells are produced only by the division of preexisting cells.
Eminent Zoologist # 4. T. Schwann (1810-1882):
Theodor Schwann, a German zoologist postulated cell theory in 1839 from his detailed study of the animal tissue. The contributions of Schleiden on the structure of plant tissues influenced his idea greatly. The cells were regarded as the structural units of a living body and tissues were made up of cells. He first used the term ‘Cell theory’ and presented it to the scientific world.
His important contributions are:
1. Every organism is made up of organic units, the cells.
2. Every organism begins life from a single cell.
3. New cells are always produced by the division of preexisting cells.
4. Experiments on spontaneous origin of life.
5. Fermentation is carried by microorganisms (bacteria).
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6. Discovery of a sheath (Sheath of Schwann) in nerve fibre.
Eminent Zoologist # 5. J. B. Lamarck (1774-1829):
Jean Baptiste de Lamarck, a French scientist, is the most pathetic figure in the evolutionary history. He was a man of vision, with the power of keen observation and logical deduction but suffered a setback mainly for his struggle with poverty and bitter criticism from his contemporaries.
He came from an army family and fought many battles. He was meant for church but religious studies could not interest him. He began his carrier as a botanist, but became a zoologist when he was offered an appointment in zoology at the Jardin des Plantes.
Lamarck’s contributions to general zoology are manifold, although his name is usually associated with the theory of organic evolution. He came very close to the cell theory of Schleiden and Schwann, thirty-nine years before they postulated it.
He extensively studied invertebrates, greatly improved classification and reorganized vertebrates and invertebrates as distinct sections of the animal kingdom. He was also a distinguished anatomist and palaeontologist.
Lamarck conceived that species were not constant, but rather were derived from preexisting species. To account for this he advocated the theory of inheritance of acquired characters and the laws of use and disuse. He was the first to give the idea of the ‘tree of life’.
Eminent Zoologist # 6. C. Darwin (1809-1882):
Charles Robert Darwin, an English scientist is famous for his theory of ‘Natural Selection’. He closely studied for long years a large number of animals belonging to different classes, plants and fossils and collected a huge volume of data. He published his famous book. “The Origin of Species by Natural Selection or the Preservation of Favoured Races in the Struggle for Life”, in the year 1859.
Evolution by natural selection, as conceived by Darwin, can be fully summarized in three points:
(i) All plants and animals reproduce in excess of the numbers which can actually survive, and this leads to a struggle for survival.
(ii) The members of the same species vary, some of the variations are neutral, while others help or hinder the organism in its struggle for survival.
(iii) As a consequence, ‘the survival of the fittest’ variants is expected, with the less fit variants being destroyed either by their physical or biotic environments.
Darwin postulated two other theories of much less importance, ‘Artificial Selection’ and ‘Sexual Selection’. For his notable contributions and popularization of biology he is also known as ‘Father of Biology’.
Eminent Zoologist # 7. H. de Vries (1848-1935):
Hugo de Vries, a Dutch botanist, published ‘Mutation theory’ in 1901. The theory is based mainly on his experiment on the plant, evening primrose, Oenothera lamarckiana. Certain strikingly different forms appeared suddenly among a population of normal type of primrose. On cultivation he recognised appearance of seven types that breed true.
He called them mutants. Starting with nine plants from the field and growing them for eight years de Vries found that the same seven mutants, appeared from the stock parental forms, year after year.
Today, it is well-known that a mutant is a true breeding variant which arises abruptly among normal forms and the mutation is a sudden measurable change in organisms which can be transmitted to the offspring’s, de Vries opened a new period of investigation on the phenomenon of heredity. He made important contributions to the study of origin of species.
Although, de Vries formulated an extremely important theory which stands well-established today, the material on which his theory was based, was later found to be rather abnormal.
Even de Vries had noticed that O. lamarckiana was an inconsistent species, de Vries proved his theory with a very unnatural species but the facts do not anyway diminish the importance of the theory. He also developed the Theory of Pangenesis. Pangenes are the materials that remain within the nucleus, multiply and come out of the nucleus to determine the form and activity of tissue.
Eminent Zoologist # 8. G. Mendel (1822-1884):
Gregor Johan Mendel, an Austrian monk, and abbot of the Augustinian Monastery at Brunn, Austria, is pioneer in the field of Heredity. Painstakingly for years he carried experiments on inheritance of characters with pure races of garden peas and from the results he deduced certain fundamental laws of heredity. These are known as ‘Law of dominance’, ‘Law of segregation’ and ‘Law of independent assortment’.
His findings were published in 1886 in an obscure journal and were made known to the world only in 1900, sixteen years after his death by three scientists Correns, de Vries and Tschermak who had independently reached the same conclusion.
The discovery of Mendel’s work gave tremendous impetus to the study of heredity and many new fields have been explored. Genetics, from a humble beginning in the hands of Mendel, ‘Father of genetics, has risen to a tremendous height and it has helped us to understand many of the problems of inheritance, and explain the complicated process of organic evolution.
Eminent Zoologist # 9. L. Pasteur (1822-1895):
The French scientist, Louis Pasteur is regarded as the founder of modern bacteriology. He discovered causative organisms of wine fermentation and the theory of ‘Spontaneous Origin’ was finally disposed. He and Joubert identified first pathogenic anaerobe Vibrion septique, and established distinction between aerobic and anaerobic bacteria.
He experimented with attenuated virus in chicken cholera, confirmed Koch’s work on Anthrax, and was pioneer in developing attenuated bacterial culture with Chamberland and Roux for therapeutically use. They discovered rabies virus in the blood and first used attenuated vaccine as a prophylactic (1885). The ‘Pasteur Institute’ in Paris was established for his investigations.
Eminent Zoologist # 10. H. Spemann (1860-1941):
Hans Spemann, an eminent German experimental embryologist performed a series of experiments on differentiation of eggs during cleavage and gastrulation. He tightly tied newt’s egg through its first cleavage furrow with human hair (1901-1903).
During subsequent division the upper half produced a miniature whole embryo whereas the other half developed into an undifferentiated ball of living cells. Spemann concluded that during first cleavage, the upper half of the egg becomes equipped with quality to form an embryo whereas the other half lacks it.
In 1918, he made another experiment on triton egg. He transplanted a small piece of ectoderm of one early gastrula to another gastrula of same age. The transplanted piece developed in accordance with at the new position. But the dorsal lip of the blastopore of amphibia grafted in similar manner, developed an embryo-like body with neural tube, notochord and somite’s.
Spemann inferred that the dorsal lip of the blastopore was already determined as centre of differentiation. He called the dorsal lip of blastopore as ‘organizer’. The discovery of concept of organizer action helps the experimental embryologists in many ways in recent times.
Eminent Zoologist # 11. T. H. Morgan (1866-1945):
Thomas Hunt Morgan, a Nobel Laureate was born at Kentucky. He entered John Hopkins University—named after the great biochemist—in 1886, after completing his undergraduate studies at Kentucky College and studied Embryology.
He got Ph.D. degree in 1890 and then joined Brym Mowr as Associate Professor of Biology in 1891. Then he joined as a Professor of Experimental Biology at Columbia University in 1909 and maintained their till his death in 1945.
Morgan was interested in embryology and the process of differentiation at the beginning of his research career but later he turned to genetics. The work of Morgan and his distinguished associates are major contribution in heredity after Mendel. Morgan formulated many genetic principles, which accelerated investigations on hereditary mechanism.