Gastrulation in animals Gastrulation is the process through which the three primary germ layers- ectoderm, mesoderm and endoderm are ultimately segregated. The blastula possesses polarity, and bilateral symmetry. It contains predetermined cell area, which would become the future ectoderm, mesoderm, endoderm, notochord and the neural plate. GASTRULATION IN AMPHIOXUS The animal pole of the blastula corresponds roughly to the front […]

Cleavage in animals The fertilized ovum enters on a series of cell division. The initial period, the development of a new multicellular individual is called the cleavage period. The process of cellular division without growth is called cleavage. During the period, the zygote split up into a number of smaller cells called the blastomeres. The

Fertilization in Animals The sperm can enter the ovum at any point on its circumference. In many mammals, entire sperm is known to pass into the cytoplasm of the ovum. After the entry of the sperm, the second polar body is extruded and the chromosomes, which remain in the ovum, reconstitute themselves into a vesicular

Anatomy of ovulation is the process and structure involved in release of ovum from the follicles in the ovary.

Polarity and Membranes of Egg Polarity of Eggs The egg consists of two poles namely animal and vegetal pole. The animal pole is the one where the nucleus of the egg lies. The opposite pole, where the yolk is accumulated is called the vegetal pole. This type of arrangement is seen in amphibians, reptiles, and

Classification of Eggs in Animals The animal eggs are classified according to the following criteria- Amount of yolk, Distribution of yolk, Presence or absence of shell and Type of development. According to the amount of yolk Alecithal: Yolk is absent. If present, it is in a negligible quantity. E.g. Mammals. Microlecithal: The eggs containing small amount of yolk and

Comparison between spermatogenesis and oogenesis Spermiogenesis Oogenesis Occurs in germinal epithelium of testes. Occurs in germinal epithelium of ovary. It involves 3 phases namely multiplication, growth and maturation phases. It involves 3 phases namely multiplication, growth and maturation phases. Meiotic divisions are equal. Meiotic divisions are unequal. At the end of the II meiotic division

Oogenesis in animals is the process by which the female gamete or ova is produced.

The development of sperm in the testes is called spermatogenesis. The testis is a glandular organ composed of several coiled seminiferous tubules and their wall is formed by a multi-layered epithelium called germinal epithelium.

Gametogenesis in Animals The process by which the gametes are produced is known as gametogenesis. the most important characteristic of every living organism is the ability to reproduce to perpetuate the species. The reproductive cells, which unite to form the new individual, are known as gametes. In all higher vertebrates, the gametes from male are called