 Chapter 47 ~
Animal
Development

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Preformation ~ until 18th century; miniature infant in sperm or egg
At fertilization/conception :
Acrosomal reaction ~ hydrolytic enzyme action on egg jelly coat….
Fast block to polyspermy
~ membrane depolarization prevents multiple fertilizations….
Cortical reaction ~ release of calcium causes hardening of egg outer layer and creates a...
Slow block to polyspermy and...
Egg activation ~ increases metabolic activity; protein synthesis

 Blastomeres~ resultant cells of cleavage/mitosis
 Yolk
~ nutrients stored in the egg
 Vegetal pole
~ side of egg with high yolk concentration
 Animal pole
~ side of egg with low yolk concentration
 Morula~ solid ball of cells
 Blastocoel
~fluid-filled cavity in morula
 Blastula
~hollow ball stage of development

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 Gastrula
~ 2 layered, cup-shaped embryonic stage
 3 Embryonic germ layers:
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Ectoderm~ outer layer; epidermis; nervous system , etc.
Endoderm ~ inner layer; digestive tract and associated organs; respiratory, etc.
Mesoderm ~skeletal; muscular; excretory, etc.
 Invagination ~ gastrula buckling process to create the...
 Archenteron ~ primitive gut
 Blastopore ~ open end of archenteron

 Blastodisc
~ cap of cells on top of yolk
 Primitive streak
~ invagination of blastodisc
 Neural tube
~ beginning of spinal cord
 Somites~ vertebrae and skeletal muscles
 Neural crest
~ bones and muscles of skull

 Extraembryonic membranes :
•yolk sac
(support; circulatory function)
•amnion
(fluid-filled sac; protection)
•chorion
(placenta formation)
•allantois
(nitrogenous waste)