| 21. | The newly hatched larvae are not very well developed and obtain nutrients from a yolk sac.
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| 22. | In " Berghia stephanieae " the development is lecithotrophic ( feed off a yolk sac ).
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| 23. | These live off the yolk sac for about twenty-four days before settling and starting filter feeding.
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| 24. | Early in development, the human embryo has three germ layers and abuts an embryonic yolk sac.
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| 25. | By the time the embryo is across, it has fully resorbed its yolk sac and external gills.
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| 26. | These two layers are sandwiched between two balloons : the primitive yolk sac and the amniotic cavity.
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| 27. | The external yolk sac is entirely absorbed when the embryo is long and close to being born.
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| 28. | Upon hatching, the benthic larvae are largely immobile and defenseless until the absorption of their yolk sac.
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| 29. | Active and term by a yolk sac.
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| 30. | As far as known, they are ovoviviparous, with the developing fetuses primarily sustained by large yolk sacs.
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