The more developed form of viviparity is called placental viviparity; mammals are the best example, but it has also evolved independently in other animals, such as in scorpions, some sharks, and in velvet worms. Viviparous offspring live independently and require an external food supply from birth. Certain lizards also employ this method such as the genera Tiliqua and Corucia. The placenta is attached directly to the mother in these lizards which is called viviparous matrotrophy.Ovoviviparous animals develop within eggs that remain within the mothers body up until they hatch or are about to hatch. It is similar to viviparity in that the embryo develops within the mothers body. Unlike the embryos of viviparous species, ovoviviparous embryos are nourished by the egg yolk rather than by the mothers body. However, the mothers body does provide gas exchange. The young of ovoviviparous amphibians are sometimes born as larvae, and undergo metamorphosis outside the body of the mother.The fish family Syngnathidae has the unique characteristic whereby females lay their eggs in a brood pouch on the males chest, and the male incubates the eggs. Fertilization may take place in the pouch or before implantation in the water. Included in Syngnathidae are seahorses, the pipefish, and the weedy and leafy sea dragons. Syngnathidae is the only family in the animal kingdom to which the term "male pregnancy" has been applied. See also
Evolution of mammals (for the evolution of gestation-related features in humans and other mammals)
Male pregnancy
Nesting instinct
Pregnancy
Pregnancy in fish
Prenatal development
Prenatal nutrition and birth weight

References
External links
NSRL.ttu.edu
Table listing average animal gestation periods
Hispanics, especially those under the age of 20, are at the highest risk for leukemia, while whites, Native Americans, Asian Americans, and Alaska Natives are at higher risk than African Americans.More men than women are diagnosed with leukemia and die from the disease. Around 30 percent more men than women have leukemia. UK
Overall, leukemia is the eleventh most common cancer in the UK (around 8,600 people were diagnosed with the disease in 2011), and it is the ninth most common cause of cancer death (around 4,800 people died in 2012). History
Leukemia was first described by anatomist and surgeon Alfred-Armand-Louis-Marie Velpeau in 1827. A more complete description was given by pathologist Rudolf Virchow in 1845. Around ten years after Virchows findings, pathologist Franz Ernst Christian Neumann found that the bone marrow of a deceased person with leukemia was colored "dirty green-yellow" as opposed to the normal red. This finding allowed Neumann to conclude that a bone marrow problem was responsible for the abnormal blood of people with leukemia.By 1900, leukemia was viewed as a family of diseases as opposed to a single disease. By 1947, Boston pathologist Sidney Farber believed from past experiments that aminopterin, a folic acid mimic, could potentially cure leukemia in children. The majority of the children with ALL who were tested showed signs of improvement in their bone marrow, but none of them was actually cured. This, however, led to further experiments.In 1962, researchers Emil J. Freireich, Jr. and Emil Frei III used combination chemotherapy to attempt to cure leukemia.