Lec.2
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Theories of Embryology
Preformation theory
During seventeenth century a Dutch scientist
Swammerdam(1637-80)theorized that sex – cells contained
preformed embryos or miniatures of the adult.
Theory of Epigenesis
This theory assumes that embryonic development and
differentiation originate in a homogeneous mass of living matter
in which there is no preformed material, neither tissues nor
organs. This theory is very old.
Baer’s Law
k.E.von Baer (1792-1876) contributed much to the field of
embryology. His investigations are tremendous. After a through
study of the development of various animals, von Bear arrived
at four important conclusions, which are collectively known as
the laws of von Baer.
The biogenetic Law or the recapitulation theory
This theory was postulated by Ernst Hackel (1868) and Muller
(1864) .It is a modified theory of Baer’s law. It is based on the
contributions of evolutionary theory.
Weismann germplasm theory
In his studies in insect and other eggs of the invertebrate animals
, Weismann discovered that the primordial germ cells which are
destined to give rise to the gonads of the organism are
segregated very early in cleavage, and that they contain all the
hereditary determinants necessary for the development of
another individual.
The Experimental Embryology
Wilhelm His, the first experimental embryologist attacked the
Biogenetic law or Haeckel vehemently. He pointed out that the
causative agent for the development and differentiation of cells,
tissues and organs could never be located by mere speculation
along phylogenetic lines.