Animal Development

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The neural plate soon curves inward, forming the neural tube. The neural tube will become the central nervous system = brain and spinal cord.

Neural crest cells develop along the neural tube of vertebrates and form various parts of the embryo: nerves, parts of teeth, skull bones .

Mesoderm lateral to the notochord forms blocks called somites.

Lateral to the somites, the mesoderm splits to form the coelom.

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Organogenesis in a chick embryo is similar to that in a frog

Endoderm

(a) Early organogenesis

Neural tube

Coelom

Notochord

These layers form extraembryonic membranes

YOLK

Heart

Eye

Neural tube

Somite

Archenteron

Mesoderm

Ectoderm

Lateral fold

Yolk stalk

Yolk sac

(b) Late organogenesis

Somites

Forebrain

Blood vessels

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Adult derivatives of the three embryonic germ layers in vertebrates

ECTODERM

MESODERM

ENDODERM

Epidermis of skin and its derivatives (including sweat glands, hair follicles) Epithelial lining of mouth and anus Cornea and lens of eye Nervous system Sensory receptors in epidermis Adrenal medulla Tooth enamel Epithelium of pineal and pituitary glands

Notochord Skeletal system Muscular system Muscular layer of stomach and intestine Excretory system Circulatory and lymphatic systems

Reproductive system (except germ cells)

Dermis of skin Lining of body cavity Adrenal cortex

Epithelial lining of digestive tract Epithelial lining of respiratory system Lining of urethra, urinary bladder, and reproductive system Liver Pancreas Thymus Thyroid and parathyroid glands

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Developmental Adaptations of Amniotes

Embryos of birds, other reptiles, and mammals develop in a fluid-filled sac in a shell or the uterus.

Organisms with these adaptations are called amniotes.

Amniotes develop extra-embryonic membranes to support the embryo.

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Amniote ExtraEmbryonic Membranes

During amniote development, four extraembryonic membranes form around the embryo:

The chorion outermost membrane / functions in gas exchange.

The amnion encloses the amniotic fluid.

The yolk sac encloses the yolk.

The allantois disposes of nitrogenous waste products and contributes to gas exchange.

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ExtraEmbryonic Membranes in birds and other reptiles:

Embryo

Amnion

Amniotic cavity with amniotic

fluid

Shell

Chorion

Yolk sac

Yolk (nutrients)

Allantois

Albumen

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