Miraculous Multiple Births Essay Research Paper Multiple

Miraculous Multiple Births Essay, Research Paper

Multiple Birth, birth of more than one offspring at a time, occurring regularly in most mammals, and uncommonly in some of the larger ones, such as cattle, horses, and humans. In humans, the tendency to bear more than one offspring is hereditary (see Heredity), and a mother who gives birth to twins is likely to have additional twins. Similarly, a twin-bearing mother stands a greater chance of producing triplets. The recent use of hormones and drugs to treat female sterility has increased the incidence of multiple birth, sometimes resulting in premature delivery of five or six offspring.

Multiple births in human beings arise either from the simultaneous impregnation of more than one ovum or from the impregnation of a single ovum that divides into two or more parts, each of which develops into a distinct embryo (see Egg; Embryology; Reproduction). Plural offspring developing from a single egg are known as identical; they are always of the same sex, resemble one another very closely, and have similar fingerprints and blood types. Offspring produced from separate ova are fraternal; not necessarily of the same sex, they have the usual family resemblance of brothers and sisters.

Twins are the most frequent form of multiple birth in humans, and identical twins occur only one-fourth as frequently as fraternal twins. In the U.S. one birth in approximately 87 is a twin birth. Triplets are about 87 times rarer than twins, and quadruplets about 87 times rarer than triplets. Quintuplets occur in about 1 out of 8 million pregnancies. These figures are for spontaneously occurring pregnancies. When ovulation has been induced by drugs, the incidence rises. Multiple births may be achieved artificially by implanting in the uterus several ova fertilized in vitro (see Infertility).

The prenatal and infant mortality rate in multiple pregnancies is higher than that in single gestations. The danger of premature birth increases progressively with the number of offspring involved.

Opossum, common name for any of 77 marsupial mammals found only in the western hemisphere. The opossum ranges in length from 17 to 104 cm (7 to 41 in), including the tail, which is from 9 to 54 cm (4 to 21 in) long. The common Virginia opossum is the largest of the opossums, measuring 109 cm (43 in), of which one-half is tail. The front feet have five toes with claws; on the hind feet the outer four toes bear claws, and the inmost toe is opposable, like a thumb, and nailless. The Virginia opossum is covered with long, sleek, white hair and an undercoating of soft, woolly fur. It has a pointed, slender face and large, broad, naked ears. An opossum has 50 teeth. Most species are omnivorous, usually preferring a diet of insects and carrion. They are nocturnal, sleeping in a burrow during the day and hunting food at night; most are arboreal. The yapock, or water opossum, of South America is aquatic, having webbed hind feet for swimming. The Virginia opossum’s habit of feigning death when threatened has given rise to the expression “playing possum.”

Most species have the abdominal pouch characteristic of marsupials; however, in some South American species this pouch is rudimentary or absent. A female opossum may have as many as 17 nipples within the pouch, but 13 is the usual number. Of the 4 to 24 young that may be born in a litter, only 8 or 9 usually survive. The gestation period is about 13 days, and the newborn opossums, about 1.4 cm (about 0.55 in) long and weighing about 0.16 g (about 0.0056 oz), are quite undeveloped. They must spend about two months in the mother’s pouch attached to the nipples before they are able to move about.

The Virginia opossum, found throughout the eastern United States and occasionally in the western states, is edible and considered a delicacy in the South. Opossum fur formerly had commercial value but is little used now. The name opossum is frequently shortened to possum, although the name possum is also used in reference to certain Australasian marsupials unrelated to opossums.


Scientific classification: Raccoons make up the genus Procyon of the family Procyonidae. The common North American raccoon is classified as Procyon lotor, and the crab-eating raccoon as Procyon cancrivorus. They are not marsupials because they do not have pouches for their new born.



Все материалы в разделе "Иностранный язык"

ДОБАВИТЬ КОММЕНТАРИЙ  [можно без регистрации]
перед публикацией все комментарии рассматриваются модератором сайта - спам опубликован не будет

Ваше имя:


Хотите опубликовать свою статью или создать цикл из статей и лекций?
Это очень просто – нужна только регистрация на сайте.

Copyright © MirZnanii.com 2015-2018. All rigths reserved.