egg
Section through a fertilized bird egg. Inside a bird's egg is a complex structure of liquids and membranes designed to meet the needs of the growing embryo. The yolk, which is rich in fat, is gradually absorbed by the embryo. The white of the egg provides protein and water. The chalaza is a twisted band of protein which holds the yolk in place and acts as a shock absorber. The airspace allows gases to be exchanged through the shell. The allantois contains many blood vessels which carry gases between the embryo and the outside.
In animals, the ovum, or female gamete (reproductive cell).
After fertilization by a sperm cell, it begins to divide to form an embryo. Eggs may be deposited by the female (ovipary) or they may develop within her body (vivipary and ovovivipary). In the oviparous reptiles and birds, the egg is protected by a shell, and well supplied with nutrients in the form of yolk.
EGG
| Mass of relatively dense interstellar gas from which gas is ‘evaporating’, or being driven off, by radiation from nearby stars. (This process has nothing to do with evaporation that we are familiar with in everyday life – for example, the drying up of a puddle of water, which is due to the loss of gas as the liquid absorbs heat energy.) |
| EGGs were so named by the US astronomer Jeff Hester in 1995 when he observed distinctive objects in spectacular photographs of the Eagle Nebula taken by the Hubble Space Telescope. Some of these EGGs lie at the tips of fingerlike structures emerging from the main mass of gas and dust. Each finger consists of gas that lies in the shadow of an EGG and so is not ‘evaporating’. Other EGGs have become isolated from the main gas cloud as gas in their immediate vicinity has been driven off. |
| In regions of the Galaxy where there are many hot young stars, their radiation blows interstellar gas away, leaving pockets of denser gas that ‘boil off’ more slowly; these are EGGs. The term is especially appropriate because inside the clump of gas there develops a protostar, or embryonic star. A protostar is hot but is not yet a star because it has not yet begun to use up hydrogen in nuclear reactions. In regions not bathed by intense radiation from nearby hot young stars, such protostars develop into stars and the clouds of gas and dust around them may develop into systems of planets. However, the prospects for this development in an EGG are not good, as material is stripped from it by the radiation from the neighbouring stars. |
Egg
| Online bank launched in the UK by Prudential plc in October 1998 as an Internet-only bank, offering low-interest-rate savings accounts, mortgages, and personal loans. In May 2007 Citigroup acquired Egg from Prudential plc. |
)
