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What is an animal?
Animals are multicellular,
heterotrophic eukaryotes with
tissues that develop from embryonic
layers.
How do animals
differ
from plants?
Animals lack cell walls and have
have collagen as their most
abundant protein.
Animals have nerve and muscle cells.
Animals have three distinct cell junctions: tight junctions, desmosomes,
and gap junctions.
A Traditional View of Animal Diversity
Based on Body-Plan Grades
Body
Symmetry
in Animals
Body
Plans
of the
Bilateria
Early Embryonic Development
Animal Phylogeny Based on
Sequencing of SSU-rRNA
Protostomes
vs.
Deuterostomes
Indeterminate
cleavage means
the cells in the
early divisions retain
the capacity to develop
into a complete
embryo.
Sea Urchin Development From
Single Cell to Larva
The Acrosomal and Cortical Reactions
During Sea Urchin Fertilization
• Cleavage partitions the cytoplasm
of one large cell into many
smaller cells called blastomeres
(a) Fertilized egg. Shown here is the (b) Four-cell stage. Remnants of the (c) Morula. After further cleavage
mitotic spindle can be seen
divisions, the embryo is a
zygote shortly before the first
between
the
two
cells
that
have
multicellular ball that is still
cleavage division, surrounded
just
completed
the
second
surrounded by the fertilization
by the fertilization envelope.
cleavage
division.
envelope. The blastocoel cavity
The nucleus is visible in the
has begun to form.
center.
Figure 47.7a–d
(d) Blastula. A single layer of cells
surrounds a large blastocoel
cavity. Although not visible here,
the fertilization envelope is still
present; the embryo will soon
hatch from it and begin swimming.
Fertilization in Mammals
Cleavage in an Echinoderm (sea
urchin) Embryo
Cleavage in a Frog Embryo
Cross Section of a Frog Blastula
Gastrulation in a Frog Embryo
• The three layers produced by
gastrulation are called embryonic
germ layers
• The ectoderm forms the outer
layer of the gastrula
• The endoderm lines the
embryonic digestive tract
• The mesoderm partly fills the
space between the endoderm and
ectoderm
• Organogenesis in the chick
is quite similar to that in the frog
Eye
Forebrain
Neural tube
Notochord
Somite
Heart
Coelom
Archenteron
Endoderm
Mesoderm
Lateral fold
Blood
vessels
Ectoderm
YOLK
Yolk stalk
Somites
Yolk sac
Form extraembryonic
membranes
(a) Early organogenesis. The archenteron forms when lateral folds (b)
pinch the embryo away from the yolk. The embryo remains open
to the yolk, attached by the yolk stalk, about midway along its length,
as shown in this cross section. The notochord, neural tube, and
somites subsequently form much as they do in the frog.
Figure 47.15a, b
Neural tube
Late organogenesis. Rudiments of most
major organs have already formed in this
chick embryo, which is about 56 hours old
and about 2–3 mm long (LM).
• Many different structures are derived
from the three embryonic germ
layers during organogenesis
ECTODERM
• Epidermis of skin and its
derivatives (including sweat
glands, hair follicles)
• Epithelial lining of mouth
and rectum
• Sense receptors in
epidermis
• Cornea and lens of eye
• Nervous system
• Adrenal medulla
• Tooth enamel
• Epithelium or pineal and
pituitary glands
Figure 47.16
MESODERM
• Notochord
• Skeletal system
• Muscular system
• Muscular layer of
stomach, intestine, etc.
• Excretory system
• Circulatory and lymphatic
systems
• Reproductive system
(except germ cells)
• Dermis of skin
• Lining of body cavity
• Adrenal cortex
ENDODERM
• 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