Sunday, January 21, 2007

Colossus of Rhodes

The Colossus of Rhodes was a giant statue of the god Helios, erected on the Greek island of Rhodes by Chares of Lindos, a pupil of Lysippos, between 292 BC and 280 BC. It was roughly the same size as the Statue of Liberty in New York, although it stood on a lower platform. It was one of the Seven Wonders of the World.

Alexander the Great died at an early age in 323 BC without having had time to put into place any plans for his succession. Fighting broke out among his generals, the Diadochi, with three of them eventually divides up much of his empire in the Mediterranean area. During the fighting Rhodes had sided with Ptolemy, and when Ptolemy eventually took control of Egypt, Rhodes and Ptolemaic Egypt formed an alliance which controlled much of the trade in the eastern Mediterranean. Another of Alexander's generals, Antigonus I Monophthalmus, was upset by this turn of events. In 305 BC he had his son Demetrius invade Rhodes with an army of 40,000. However, the city was well defended, and Demetrius had to start construction of a number of massive siege towers in order to gain access to the walls.

Monday, January 08, 2007

Identical twins

Identical twins occur when a single egg is fertilized to form one zygote which then divides into two separate embryos. This is not considered to be a hereditary trait, but rather an anomaly that occurs in birthing at a rate of about 1:150 births worldwide, regardless of ethnic background. The two embryos develop into fetuses sharing the same womb. When one egg is fertilized by one sperm cell, and then divides and separates, two identical cells will result. Depending on the stage at which the zygote divides, identical twins may share the same amnion, which can cause complications in pregnancy.

For example, the umbilical cords of monoamniotic twins can become entangled, reducing or interrupting the blood supply to the developing fetus. About 50% of mono-mono twins die from umbilical cord entanglement. Monochorionic twins, sharing one placenta, usually also share the placental blood supply. These twins may develop such that blood passes disproportionately from one twin to the other through connecting blood vessels within their shared placenta, leading to twin-to-twin transfusion syndrome.

Monday, January 01, 2007


Metamorphosis is a biological course by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's form or structure through cell growth and differentiation. Some insects, amphibians, molluscs, crustaceans, echinoderms and tunicates undertake metamorphosis, which is usually accompanied by a change of habitat or behavior. Scientific usage of the term is exclusive, and is not applied to common aspects of growth, including rapid growth spurts. References to “metamorphosis” in mammals are imprecise and only colloquial.

Metamorphosis usually proceeds in distinct stages, usually starting with larva or nymph, optionally passing through pupa, and ending as adult. The immature stages of a species that metamorphoses are regularly called larva. But in the complex metamorphosis of many insect species, only the first stage is called a larva and sometimes even that bears a different name; the distinction depends on the nature of the metamorphosis.