After 45 hours, 12-18 tiny cells are seen in the cytoplasm of the zygote. A nucleus enters each segment. They are arranged in two layers like petals. This condition is called rosette. Each part, including the nucleus, becomes a merozoite. Merozoites invade new red blood cells. During this time, a large amount of chemical substances called pyrogen accumulates in the blood and due to its effect, fever occurs in the body.