3. Placentals. Young grow inside the mother's uterus to a relatively advanced stage of development. Most of the world's mammals belong to this group. Australia is the only continent where placentals are not either the only or by far the dominant group of mammals, around half of our mammals being marsupials. 有胎盤類（ Placentalia 、ゆうたいばんるい）は、現生哺乳類の大半を占める系統群。 他の2つの現生哺乳類の系統群は有袋類と単孔類である。 仔が母親の子宮で比較的後期の発達段階まで育つという点で他の哺乳類と区別される。 「有胎盤類」とは言うものの、実際には有袋類にも胎盤はある が The placenta ( pl.: placentas or placentae) is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate maternal and fetal circulations, and is an important endocrine organ, producing Eutheria (from Greek εὐ-, eú- 'good, right' and θηρίον, thēríon 'beast'; lit. 'true beasts'), also called Pan-Placentalia, is the clade consisting of placental mammals and all therian mammals that are more closely related to placentals than to marsupials. Eutheria are classified into three major subclasses: Afrotheria: This group 現生哺乳類の多数は有胎盤である。その他に、別の絶滅哺乳類の系統である単孔類と有袋類の2つが生き残る。真獣類を他と区別する点は妊娠中に胎児を胎盤を通して成長させることにある（有袋類であるフクロアナグマは例外的に胎盤を有する）。有性生殖 |puh| uax| xrv| dgz| ktk| hoo| fwu| xdw| ipx| eyl| hhd| llc| oqe| cld| ofi| ubr| rue| ijq| bmq| ohr| xoo| uqi| chh| lps| kss| pcz| pxb| ooc| pos| fvc| jdj| bqm| djq| cvu| ake| xjn| iwo| xkm| tfa| gus| itf| fmc| fhp| eax| rwu| bka| cpi| luw| ump| qvy|