Eihülle

Eihülle, also known as the egg envelope or ovum envelope, refers to the protective layers surrounding an egg cell, or ovum. In biological terms, it is a crucial component of the female gamete, playing significant roles in fertilization and early embryonic development. The specific composition and structure of the eihülle can vary considerably between different species, reflecting their diverse reproductive strategies and evolutionary paths.

For instance, in many vertebrate species, including humans, the eihülle is composed of the zona pellucida, a thick glycoprotein layer that surrounds the plasma membrane of the oocyte. This layer serves multiple functions. It helps to select sperm during fertilization, preventing polyspermy (fertilization by more than one sperm) by undergoing a change after the first sperm penetrates. It also provides structural support to the developing embryo in its early stages. Outside the zona pellucida, there is often a layer of follicular cells, known as the corona radiata, which provides nourishment and further protection to the oocyte.

In contrast, organisms like insects or birds have different forms of egg envelopes. Bird eggs, for example, are enclosed by a hard, calcified shell that offers significant protection from the external environment and allows for gas exchange. Within this shell are membranes and the albumen (egg white), which further contribute to the protection and nourishment of the developing embryo. The diversity in eihülle structures highlights the evolutionary adaptations that facilitate successful reproduction in a wide range of organisms.