章节大纲

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  • Marsupial 义体

    A koala perched on a tree branch, showcasing its characteristic gray fur and round ears.

    Is it really a bear?
    ::真的是熊吗?

    The koala. Or sometimes called the koala bear. The koala is a marsupial native to Australia. And it is very different t o any other bear.
    ::考拉,或者有时叫做考拉熊,考拉是澳大利亚土生土长的马苏比人。它与其他熊非常不同。

    Marsupials
    ::Marsupial 义体

    Marsupials have a different way of reproducing that reduces the mother’s risks. A marsupial is a therian mammal in which the embryo is born at an early, immature stage. The embryo completes its outside the mother’s body in a pouch on her belly. Only a minority of therian mammals are marsupials. They live mainly in Australia. Examples of marsupials are pictured in Figure .
    ::Marsupial有不同的繁殖方式,可以减少母亲的风险。 marsupial是一种有神话的哺乳动物,胚胎在早期、不成熟的阶段出生。胚胎在母体外部的腹部用一个袋子在母体腹部上完整。只有少数少数的哺乳动物是marsupials。它们主要生活在澳大利亚。图中描绘了marsupials的例子。

    Kangaroo, koala, and Virginia opossum shown, illustrating different marsupial species.

    Marsupials. Marsupials include the kangaroo, koala, and opossum.
    ::Marsupials。 Marsupials 包括袋鼠, 考拉, 和假象。

    The Marsupial Embryo
    ::马苏比亚安布丽奥

    The marsupial embryo is nourished inside the uterus with food from a yolk sac instead of through a placenta . The yolk sac stores enough food for the short period of time the embryo remains in the uterus. After the embryo is born, it moves into the mother’s pouch, where it clings to a nipple. It remains inside the pouch for several months while it continues to grow and develop. Even after the offspring is big enough to leave the pouch, it may often return to the pouch for warmth and nourishment. Eventually, the offspring is mature enough to remain outside the pouch on its own.
    ::卵巢胚胎在子宫内养殖,食物来自蛋白囊,而不是通过胎盘。蛋白囊在胚胎留在子宫的短期内储存足够的食物。胚胎出生后,胚胎会进入母亲的邮袋,它会粘着一个乳头。它会留在袋里数月,同时会继续成长和发育。即使后代足够大,可以离开袋子,它也往往会回到袋子里取暖和营养。最终,后代已经成熟到可以自己留在邮袋外面。

    Pros and Cons of Marsupial Development
    ::火星发展的利弊

    In marsupials, the short period of development within the mother’s uterus reduces the risk of her immune system attacking the embryo. In addition, the marsupial mother doesn’t have to eat extra food or carry a large fetus inside her. The risks of giving birth to a large fetus are also avoided. Another pro is that the mother can expel the embryo from her pouch if she is pursued by a predator or if food is scarce. On the other hand, a newborn marsupial is tiny and fragile. Therefore, it may be less likely to survive than a newborn .
    ::在宫内,母亲子宫的短暂发育期降低了其免疫系统攻击胚胎的风险。此外,母亲不必多吃食物,也不携带大胎儿。生育大胎儿的风险也避免了。另一个好处是,母亲可以将胚胎从邮袋中驱逐出去,如果她被掠食者追赶或食物短缺的话。另一方面,新生儿的婚纱很小而且很脆弱。因此,它可能比新生儿更不可能存活下来。

      

     

    The North American Marsupial: The Opossum
    ::北美马苏比亚:

    Most people think of opossums as scary creatures. Is this because they look kind of funny, walk kind of funny, have beady and sharp teeth, and can emit a very foul odor? Maybe. But what is so different about opossums is that they are the only marsupial in North America.
    ::大部分人认为阴部瘤是可怕的生物。 这是因为它们看起来有点滑稽,行走方式有点滑稽,牙齿有珠子和尖锐的牙齿,能够发出非常肮脏的气味吗?也许吧。但是对于阴部瘤来说,有什么不同呢?它们是北美唯一的麻木动物。

    These opossums, however, can be beneficial to humans. They use their sharp teeth to crush – which means that they are good getting rid of unwanted rodents in your neighborhood. They have excellent immune systems and they emit that terrible odor for protection. 
    ::然而,这些假象可以对人类有益。 他们用尖锐的牙齿来粉碎 — — 这意味着他们能很好地摆脱邻里那些不受欢迎的鼠类。 他们有很好的免疫系统,他们散发了可怕的保护气味。

      

     

    Summary
    ::摘要

    • Marsupials give birth to a tiny, immature embryo. The embryo then continues to grow and develop in a pouch on the mother’s belly.
      ::马苏比亚孕育了一个很小的、不成熟的胚胎。 然后胚胎在母亲肚子上的袋子里继续生长和发育。
    • Marsupial development is less risky for the mother. However, the embryo is fragile, so it may be less likely to survive than the fetus of a placental mammal.
      ::对母亲来说,火星发育风险较小,但胚胎是脆弱的,因此,它生存的可能性可能比胎胎哺乳动物的胎儿要小。

    Review
    ::回顾

    1. What is a marsupial?
      ::什么是结婚仪式?
    2. Where does a marsupial embryo develop? How is it nourished?
      ::婚姻胚胎在哪里发育?它是如何培育的?
    3. Name two advantages of marsupial development?
      ::说明婚姻发展的两个好处吗?