Introduction of Veterinary Embryology
Veterinary Embryology is the science that deals with the origin and development of the individual organism or it deals with the formative history of animals from the time of fertilization of the female germ cell or ovum by a sperm to the adult condition. Exceptionally an ovum may develop into an organism without being fertilized by a sperm, which is known as parthenogenesis.
Historical background
- The study of Embryology becomes more interesting with discussion on the historical background of the subject. Aristotle, (384-322 B.C] Greek philosopher studied the embryos of many animals without the aid of microscope. He wrote the first treatise on embryology. He formulated that the embryo was a preformed structure and only enlarging during its development or it must be actually differentiating from a formless beginning.
- Galen (165-200 A.D) learned much about the structure of relatively advanced fetuses but the minute dimensions of early embryos was not studied due to the lack of the invention of the microscope.
- Regnier.de. Graaf (1672) described the ovarian follicles and Antony van Leeuwenhoek (1677) described the sperm of man and mammals. But significance of sperm and ovum was not known to these scientists.
- All this time two groups were emerged. According to the Homanculist or Spermatist view the sperm contained a minute individual, which grew into a fully formed baby by taking nourishment from the ovum. According to the other view, the minute human being was situated inside the ovum. The sperm merely activated its growth. This was called as the Ovist view. These views are also known as Preformation doctrine or view, which says that human being is preformed either in sperm or in ovum.
- The preformation theory was destroyed by the Spallanzani and Wolff (1759). According to them, there is no minute individuals either in a sperm or in an ovum. But the development takes place by progessive growth and differentiation of basic buildings in it known as cells. This is called as Epigenesis.
- Karl Ernst Van Baer (1828) first described the germ layers ectoderm and endoderm and he was honoured as the Father of Modern Embroyology.
- Cleavage or subdivision of the cell into the building units of the embryo was described by the Prevost and Dumas (1824). This was followed by Schleiden (1838) and Schwann (1839) who propounded the cell theory which states that the body of an organism is com posed of innumerable microscopic cells, form the tissues.
- Errnst Haeckel, (1866) a German scientist formulated the Bio-genetic law as “Ontogeny recapitulates Phylogeny”. Ontogeny means development of an individual organism whereas Phylogeny denotes the development of a race. According to this, the mammalian embryo looks like an embryo of fish and then like the embryo of reptile before the mammalian shape is obtained. The early stages of embryos of fishes, amphibians, reptiles, birds and mammals looks somewhat similar.
- Van Beneden (1883) proved that the male and female sex cells contribute the same number of chromosomes to the fertilized eggs.
Branches of embryology
Descriptive embryology
Descriptive embryology branch of study is based on the observations and descriptions of different embryonic stages of the ontogenic development of a species. It is the chief concern of the early embryologists.
Comparative embryology
Comparative studies are made between the embryology of most animal types and are classified, compared and common trends and principles are sought.
Experimental embryology
Experimental embryology is the branch of embryology that attempts to understand the fundamental development mechanisms or the factors, which active or regulate the developmental process. It is also called as developmental mechanics, casual embryology, and analytical embryology.
Chemical embryology
To understand the developmental phenomena in molecular terms, various biochemical, molecular, biological, biophysical and physiological techniques are employed to the developing embryo.
Teratology
Teratology is the study of malformations/abnormalities.
Developmental biology
Developmental biology is the study of post-natal processes such as normal growth, metamorphosis, regeneration and tissue repair at the levels of complexity ranging from the molecular to the organism level along with the embryonic development. It is the study of processes and concepts rather than specific morphological structures.
Scope of embryology
- To the student of Veterinary medicine the study of embryology is of great practical value as it helps-
- To provide a comprehensive and rational explanation of the many facts of anatomy which are otherwise meaningless or anomalous.
- To interpret rudimentary structures, variations, anomalies and monstrosities.
- To understand the origin of certain tumors and other pathological changes in tissues.
- To unlock the secrets of heredity, determination of sex and organic evolution.
- A general conception of how man and other animals develop from a single cell by orderly and logical processes should share in the cultural background of every educated mind.
