Nucleus
Source: http://nobelprize.org/nobel_prizes/medicine/laureates/1999/illpres/
The most important Eukaryotic organelle is the nucleus. A nucleus is found near the center of the cell, as you can see in the picture to the left, of a cell. The nucleus is found in both plants and animal cells. There is usually just one nucleus per cell. This one nucleus per cell contains the cell's hereidtary information and controls the cell, this is why it is known as "the brain".
Nucleolus
Source: http://micro.magnet.fsu.edu/cells/nucleus/nucleolus.html
Inside of the nucleus is what is called the nucleolus. The nucleolus is a knot of chromatin, which is DNA in its active form. As you can see in the picture to the left. Chromatin consists of DNA looped around histone proteins. The nucleulos manufactures ribosomes.
Nuclear Envelope
Source: http://micro.magnet.fsu.edu/cells/nucleus/nuclearenvelope.html
Surrounding the Nucleus is the nuclear Envelope. The nuclear envelope is a double layered membrane that envelopes the nucleus. The nuclear envelope seperates the cytoplasm from the nucleus. The nuclear envelope has many pores on it's skin along with ribosomes.