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Evolution Of Descended Testes In Mammals
Mammals are the only animals in which the testes descend from their point of origin into a scrotum. Concurrently, mammals are the only class of vertebrates to evolve a prostate gland starting with prostate evolution in monotreme mammals. Testicular descent occurs to a variable degree in various mammals, ranging from virtually no change of position from the abdominal cavity (monotremes, elephants and hyraxes); through migration to the caudal end of the abdominal cavity (armadillos, whales and dolphins); migration just through the abdominal wall (hedgehogs, mole (animal), moles, Pinniped, seals); formation of a sub-anal swelling (pigs, rodents); to the development of pronounced scrota (primates, dogs, ruminants) in mammals.Setchell B.P. (1978). The Mammalian Testis. Cornell University Press, Ithaca, New York. Since descent of the testes into a scrotal pouch subjects the animal to enhanced risk of accidental damage and/or vulnerability from predators and rivals, presumably there must b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mammals
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or hair, and three middle ear bones. These characteristics distinguish them from reptiles (including birds) from which they diverged in the Carboniferous, over 300 million years ago. Around 6,400 extant species of mammals have been described divided into 29 orders. The largest orders, in terms of number of species, are the rodents, bats, and Eulipotyphla ( hedgehogs, moles, shrews, and others). The next three are the Primates (including humans, apes, monkeys, and others), the Artiodactyla (cetaceans and even-toed ungulates), and the Carnivora (cats, dogs, seals, and others). In terms of cladistics, which reflects evolutionary history, mammals are the only living members of the Synapsida (synapsids); this clade, tog ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mole (animal)
Moles are small mammals adapted to a subterranean lifestyle. They have cylindrical bodies, velvety fur, very small, inconspicuous eyes and ears, reduced hindlimbs, and short, powerful forelimbs with large paws adapted for digging. The word “mole” refers to any species in the family Talpidae, which means “mole” in Latin. Moles are found in most parts of North America, Europe and Asia. Moles may be viewed as pests to gardeners, but they provide positive contributions to soil, gardens, and ecosystem, including soil aeration, feeding on slugs and small creatures that eat plant roots, and providing prey for other wildlife. They eat earthworms and other small invertebrates in the soil. Terminology In Middle English, moles were known as ''moldwarp''. The expression "don't make a mountain out of a molehill" (which means "exaggerating problems") was first recorded in Tudor times. By the era of Early Modern English, the mole was also known in English as ''mouldywarp'', a w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fertility
Fertility is the capability to produce offspring through reproduction following the onset of sexual maturity. The fertility rate is the average number of children born by a female during her lifetime and is quantified demographically. Fertility is addressed when there is a difficulty or an inability to reproduce naturally, which is referred to as infertility. Infertility is widespread, with fertility specialists available all over the world to assist mothers and couples who experience difficulties having a baby. Human fertility depends on factors of nutrition, sexual behaviour, consanguinity, culture, instinct, endocrinology, timing, economics, personality, way of life, and emotions. Fertility differs from fecundity, which is defined as the ''potential'' for reproduction (influenced by gamete production, fertilization and carrying a pregnancy to term). Where a woman or the lack of fertility is infertility while a lack of fecundity would be called sterility. Demograph ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Epididymis Evolution From Reptiles To Mammals
The epididymis, which is a tube that connects a testicle to a vas deferens in the male reproductive system, evolved by retention of the mesonephric duct during regression and replacement of the mesonephros with the metanephric kidney. Similarly, during embryological involution of the paired mesonephric kidneys, each mesonephric duct is retained to become the epididymis, vas deferens, seminal vesicle and ejaculatory duct (Wolffian duct). In reptiles and birds both the testes and excurrent ducts (efferent ducts, epididymis, vas deferens) occur in an intra-abdominal location ( testicond). Primitive mammals, such as the monotremes (prototheria), also are testicond. Marsupial (metatheria) and placental ( eutheria) mammals exhibit differing degrees of testicular descent into an extra-abdominal scrotum.Bedford, H.M. (1978)Anatomical evidence for the epididymis as the prime mover in the evolution of the scrotum American Journal of Anatomy 152: 483-508. In scrotal mammals the epididymis is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Epididymis
The epididymis (; plural: epididymides or ) is a tube that connects a testicle to a vas deferens in the male reproductive system. It is a single, narrow, tightly-coiled tube in adult humans, in length. It serves as an interconnection between the multiple efferent ducts at the rear of a testicle (proximally), and the vas deferens (distally). Anatomy The epididymis is situated posterior and somewhat lateral to the testis. The epididymis is invested completely by the tunica vaginalis (which is continuous with the tunica vaginalis covering the testis). The epididymis can be divided into three main regions: * The head ( la, caput). The head of the epididymis receives spermatozoa via the efferent ducts of the mediastinium of the testis at the superior pole of the testis. The head is characterized histologically by a thick epithelium with long stereocilia (described below) and a little smooth muscle. It is involved in absorbing fluid to make the sperm more concentrated. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Evolution
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation tends to exist within any given population as a result of genetic mutation and recombination. Evolution occurs when evolutionary processes such as natural selection (including sexual selection) and genetic drift act on this variation, resulting in certain characteristics becoming more common or more rare within a population. The evolutionary pressures that determine whether a characteristic is common or rare within a population constantly change, resulting in a change in heritable characteristics arising over successive generations. It is this process of evolution that has given rise to biodiversity at every level of biological organisation, including the levels of species, individual organisms, and molecules. The theory of evol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ruminants
Ruminants ( suborder Ruminantia) are hoofed herbivorous grazing or browsing mammals that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microbial actions. The process, which takes place in the front part of the digestive system and therefore is called foregut fermentation, typically requires the fermented ingesta (known as cud) to be regurgitated and chewed again. The process of rechewing the cud to further break down plant matter and stimulate digestion is called rumination. The word "ruminant" comes from the Latin ''ruminare'', which means "to chew over again". The roughly 200 species of ruminants include both domestic and wild species. Ruminating mammals include cattle, all domesticated and wild bovines, goats, sheep, giraffes, deer, gazelles, and antelopes.Fowler, M.E. (2010).Medicine and Surgery of Camelids, Ames, Iowa: Wiley-Blackwell. Chapter 1 General Biology and Evolution addresses t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Primates
Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians (monkeys and apes, the latter including humans). Primates arose 85–55 million years ago first from small terrestrial mammals, which adapted to living in the trees of tropical forests: many primate characteristics represent adaptations to life in this challenging environment, including large brains, visual acuity, color vision, a shoulder girdle allowing a large degree of movement in the shoulder joint, and dextrous hands. Primates range in size from Madame Berthe's mouse lemur, which weighs , to the eastern gorilla, weighing over . There are 376–524 species of living primates, depending on which classification is used. New primate species continue to be discovered: over 25 species were described in the 2000s, 36 in the 2010s, and three in the 2020s. Primates hav ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rodents
Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are native to all major land masses except for New Zealand, Antarctica, and several oceanic islands, though they have subsequently been introduced to most of these land masses by human activity. Rodents are extremely diverse in their ecology and lifestyles and can be found in almost every terrestrial habitat, including human-made environments. Species can be arboreal, fossorial (burrowing), saltatorial/richochetal (leaping on their hind legs), or semiaquatic. However, all rodents share several morphological features, including having only a single upper and lower pair of ever-growing incisors. Well-known rodents include mice, rats, squirrels, prairie dogs, porcupines, beavers, guinea pigs, and hamsters. Rabbits, hares, and pikas, whose inciso ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pigs
The pig (''Sus domesticus''), often called swine, hog, or domestic pig when distinguishing from other members of the genus ''Sus'', is an omnivorous, domesticated, even-toed, hoofed mammal. It is variously considered a subspecies of ''Sus scrofa'' (the wild boar or Eurasian boar) or a distinct species. The pig's head-plus-body length ranges from , and adult pigs typically weigh between , with well-fed individuals even exceeding this range. The size and weight of hogs largely depends on their breed. Compared to other artiodactyls, a pig's head is relatively long and pointed. Most even-toed ungulates are herbivorous, but pigs are omnivores, like their wild relative. Pigs grunt and make snorting sounds. When used as livestock, pigs are farmed primarily for the production of meat, called pork. A group of pigs is called a ''passel'', a ''team'', or a ''sounder''. The animal's bones, hide, and bristles are also used in products. Pigs, especially miniature breeds, are kept ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pinniped
Pinnipeds (pronounced ), commonly known as seals, are a widely range (biology), distributed and diverse clade of carnivorous, fin-footed, semiaquatic, mostly marine mammal, marine mammals. They comprise the extant taxon, extant family (biology), families Odobenidae (whose only living member is the walrus), Otariidae (the eared seals: sea lions and fur seals), and Phocidae (the earless seals, or true seals). There are 34 extant species of pinnipeds, and more than 50 extinct species have been described from fossils. While seals were historically thought to have descended from two ancestral lines, molecular phylogenetics, molecular evidence supports them as a monophyletic lineage (descended from one ancestral line). Pinnipeds belong to the order Carnivora; their closest living relatives are Musteloidea, musteloids (Mustelidae, weasels, Procyonidae, raccoons, skunks, and red pandas), having diverged about 50 million years ago. Seals range in size from the and Baikal sea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hedgehog
A hedgehog is a spiny mammal of the subfamily Erinaceinae, in the eulipotyphlan family Erinaceidae. There are seventeen species of hedgehog in five genera found throughout parts of Europe, Asia, and Africa, and in New Zealand by introduction. There are no hedgehogs native to Australia and no living species native to the Americas. However, the extinct genus '' Amphechinus'' was once present in North America. Hedgehogs share distant ancestry with shrews (family Soricidae), with gymnures possibly being the intermediate link, and they have changed little over the last fifteen million years. Like many of the first mammals, they have adapted to a nocturnal way of life. Their spiny protection resembles that of porcupines, which are rodents, and echidnas, a type of monotreme. Etymology The name ''hedgehog'' came into use around the year 1450, derived from the Middle English ''heyghoge'', from ''heyg'', ''hegge'' ("hedge"), because it frequents hedgerows, and ''hoge'', ''hogg ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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