Thinking about how animals mate, one might at first think about the way that mammals do it. But what do we know about how other animals reproduce, including those that some might find rather unattractive, like spiders? Spiders have evolved a unique way of sperm transfer: besides their four pairs of walking legs, male spiders possess an additional pair of smaller, specialized body appendages, the pedipalps (Fig. 1). An organ at the tip of the pedipalps of males, the “palpal-organ” or “copulatory bulb” (Fig. 2), is used to take up droplets of seminal fluid from a specially produced sperm web ..read more

The sponges are structurally primitive animals, very ancient as a group and only distantly related to the animals of other groups. They are multicellular but have attained relatively little histological differentiation either as regards cell types or their integration in layer and organs. Organs cen hardly be said to exist, and whole tissues characteristic of higher animals are lacking, such as nervous and muscular tissues. Specialized gland cells also are few or lacking. Indeed the body consists of a rather loose mesenohyme, which produces the skeletal elements, covered by external and inter ..read more

• Definition: The process of maturation and differentiation of PGC to oogonia, primary oocytes, secondary oocytes and to mature ova in the female genital tract.  • Location: Ovarian cortex.  • Peculiarities of oogenesis:  – Starts before birth (10th week)  – Stops in the middle (birth to puberty) – Restarts at puberty (11–13 years)  – Continues up to menopause (45–55 years)  • Processes: The various processes in oogenesis are:  – Mitosis – Meiosis  – Growth of follicles – Differentiation of follicles • The cortex contains many large round cells called “oogonia”. All the oogonia to be utiliz ..read more

The process of formation of gametes is called “gametogenesis”. The gametes are derived from primordial germ cells/ primitive sex cells.  • Primordial germ cells (PGC)/Primitive sex cells:Gametes are derived from PGC during 4th week of development. The PGC appear in the wall of yolk sac from which they migrate to the developing gonad from the coelomic epithelium and adjacent mesenchyme. The PGC undergo mitotic division during their migration resulting in increase in their number.  • Definition: Gametogenesis can be defined as the process of conversion of primordial or primitive germ cells and ..read more

• Genes are carriers of blueprints for formation of cells, tissues, organs, and organism. Genes are made up of a nucleic acid called deoxyribonucleic acid (DNA) and all information is stored in the molecules of this substance. The genes are strung together to form structures containing long chains of DNA known as chromosomes.  • Genes are involved in the synthesis of proteins. Proteins are the most important constituents of our body. They make up the greater part of each cell and of intercellular substances. Enzymes, hormones and antibodies are also proteins.  • The nature and functions of ..read more

• It is the science that deals with the processes and regulations in the prenatal growth and development of an organism/individual in the female genital tract. It begins with the fusion of male and female gametes (fertilization) in the fallopian tube up to the birth as a neonate. • Prenatal development involves repeated division of most of the cells in the body resulting in growth in size, complexity, structural and functional differentiation of body.  • Embryology includes the study of startling integration of various complex molecular, cellular and structural processes that are accountable ..read more

Development is the process where someone or something grows or changes and becomes more advanced.Human development is a continuous process that does not stop at birth. It continues after birth for increase in the size of the body, eruption of teeth, etc. Development before birth is called prenatal development, and that after birth is called postnatal development. Each period is further subdivided into several stages. Prenatal Development There are three stages in prenatal development. They are:  1. Preimplantation/pre-embryonic period  2. Embryonic period 3. Fetal period. Preimplantation/Pre ..read more

Understanding where SARS-CoV-2 -- the virus that caused the COVID-19 pandemic -- came from and how it spreads is important for its control and treatment. Most experts agree that bats are a natural reservoir of SARS-CoV-2, but an intermediate host was needed for it to jump from bats to humans. A recent study that analyzed the new virus' genome suggested snakes as this host, despite the fact that coronaviruses are only known to infect mammals and birds. Meanwhile, an unrelated study compared the sequence of the spike protein -- a key protein responsible for getting the virus into mammalian ..read more

Though all the members of animalia are multicelluler,all of them do not exhibit the same pattern of organisation of cells. for example, in sponges,the cells are arranged as loose cell aggregates,i.e.,they exhibit cellular level of organisation.some division of labour occurs among the cells. In coelentraterates,ghe arrangement of the cells is more complex.Here the cells performing the same function are arranged into tissues,hence is called tissue level of organisation. A still higher level of organisation,ie.,organ level is exhibited by members of platyhelminthes and other higher phyla where ti ..read more

Inspite of differences in structure and form of different animals,there are fundamental features common to various individuals in relation to the arrangement of cells,body,symmetry,nature of coelom,patterns of digestive,circulatory or reproductive system.These features are used as the basis of animal classification ..read more