Development of general body form and early features As a result of Gastrulation, the embryonic part of the gastrula consists of a flat structure in addition to the formation of three basic germ layers. The basic body pattern in adult vertebrate is found to have one tube within another, the outer being synonymous with the […]

Stages in Prenatal Period and Twining in Animals Stages in Prenatal Period Period of the ovum In which male and female germ meet, unite and form the zygote which develops into the blastula and gastrula covering the first 14 days of intrauterine life. Period of the embryo From end of the second week, it extends

Types of Placenta in Animals Based on Anatomical Classification The placenta is of two varieties- Deciduate and non-deciduate type. Non-deciduate further classified- Cotyledonary, Diffuse and Zonary. Deciduate Placenta in which the foetal part of the placenta is very closely associated with the maternal part and hence part of endometrium also is shed off after parturition,

Placenta of Animals Placenta is the intimate apposition or fusion of extra embryonic membranes to the maternal tissue for the physiological processes of respiration, nutrition and excretion. In addition placenta protects the embryo. Foetal membranes (or) Extra Embryonic membranes Yolk Sac The endoderm lines the inner border of the blastocyst, converting the blastocoele into the

Foetal Membranes of animals In the development of a higher vertebrate embryos like those of chick and mammals, only part of the cleavage cell mass forms the actual embryo, whereas other parts lie outside the embryonic territory and are called extra embryonic. The extra embryonic parts form foetal membranes, which are the auxiliary organs to protect the

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