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  • 单色

    An echidna, a spiny monotreme mammal, foraging on the ground among leaves.

    Can a mammal lay an egg?
    ::哺乳动物能产卵吗?

    This is a mammal . But it is unlike placental or mammals. If a mammal does not develop within a placenta or a pouch, what type of is left? Eggs!
    ::这是哺乳动物,但不同于胎盘或哺乳动物。如果哺乳动物没有在胎盘或邮袋中发育,那么剩下什么类型?蛋!

    Monotremes
    ::单色

    Only five living of mammals are not therian mammals . They are called monotremes. Monotremes are mammals that reproduce by laying eggs . The only living monotreme species are the platypus and echidnas (see Figure and Figure ). They are found solely in Australia and New Guinea (an island not far from Australia).
    ::只有5种哺乳动物不是动物哺乳动物,它们被称为单体动物。单体动物是通过产卵繁殖的哺乳动物。唯一的单体动物是白蚁和(见图和图)。它们只在澳大利亚和新几内亚(离澳大利亚不远的一个岛屿)发现。

    A platypus swimming underwater among aquatic plants.
    This egg-laying, venomous, duck-billed, beaver-tailed, otter-footed mammal is a platypus, a monotreme mammal that reproduces by laying eggs.
    An echidna, a spiny monotreme mammal, foraging on the ground.
    Like the platypus, the echidna is a monotreme. The only living monotreme species inhabit Australia and New Guinea.

    Eggs and Lactation in Monotremes
    ::单体中的卵蛋和Lactation

    Female monotremes lack a uterus and vagina . Instead, they have a cloaca with one opening, like the cloacas of and . The opening is used to excrete wastes as well as lay eggs.
    ::雌性单胞胎缺乏子宫和阴道,相反,它们有一个有开口的卡帕卡,像卡帕卡和。开口用来排出废物和产卵。

    Monotreme eggs have a leathery shell, like the eggs of reptiles. The eggs are retained inside the mother’s body for at least a couple of weeks. During that time, the mother provides the eggs with nutrients . Platypus females lay their eggs in a burrow. Echidna females have a pouch in which they store their eggs. Female monotremes have mammary glands but lack nipples. Instead, they “sweat” milk from a patch on their belly.
    ::单蛋有皮壳,就像爬行动物的卵一样。 蛋在母体内保留至少几个星期。 在此期间,母蛋提供养分。 母蛋在洞里产卵。 母蛋在洞里产卵。 雌性埃奇德纳产卵袋。 雌性单体有乳腺,但缺乏乳头。 相反,它们从腹部的一块小块中“香奶 ” 。

    Pros and Cons of Monotreme Reproduction
    ::单体生殖的利弊

    The mother’s risks are less in monotremes than in therian mammals. The mother doesn’t need to eat more or put herself at risk by carrying and delivering a fetus or an embryo . On the other hand, externally laid eggs are more difficult to protect than an embryo in a pouch or a fetus in a uterus. Therefore, monotreme offspring may be less likely to survive than the offspring of therian mammals.
    ::母亲的风险在单体动物中要小于在单体哺乳动物中。 母亲不需要通过携带和分娩胎儿或胚胎来多吃或冒风险。 另一方面,外部产卵比在袋中胚胎或子宫中的胎儿更难保护。 因此,单体后代可能比动物哺乳动物的后代更难生存。

    Summary
    ::摘要

    • Monotremes reproduce by laying eggs.
      ::单体通过产卵繁殖。
    • Monotremes have a cloaca instead of a uterus and vagina. The eggs pass through the opening of the cloaca.
      ::单体有木薯而不是子宫和阴道 鸡蛋穿过木薯的开口
    • Monotreme reproduction is the least risky for the mother. However, eggs are harder to protect than is an embryo or a fetus in a pouch or uterus. Therefore, monotreme offspring may have a lower chance of surviving than the offspring of therian mammals.
      ::单体生殖对母亲来说风险最小,但是,蛋比胚胎或胎儿在袋中或子宫中更难保护,因此,单体后代存活的可能性可能比动物哺乳动物的后代小。

    Review
    ::回顾

    1. What are monotremes?
      ::什么是单体?
    2. Describe eggs and egg laying in monotremes.
      ::描述在单体内产卵和产卵。
    3. How does lactation differ in monotremes and therian mammals?
      ::哺乳动物在单体哺乳动物和原生哺乳动物方面有何不同?
    4. Create a chart that you could use to explain to a younger student the different ways that mammals reproduce.
      ::创建一个图表,你可以用来向年轻学生解释 哺乳动物繁殖的不同方式。