The process of cytokinesis in animal cells, characterized by pinching of the plasma membrane.
A hollow ball of cells that marks the end of the cleavage stage (128 cells); indeterminate.
In animal development, a series of cell and tissue movements in which the blastula-stage embryo folds inward, producing a three-layered embryo, the gastrula.
An embryonic stage in animal development encompassing the formation of three layers: ectoderm, mesoderm, and endoderm.
A free-living, sexually immature form in some animal life cycles that may differ from the adult animal in morphology, nutrition, and habit.
A developmental transformation that turns an animal larva into either an adult or an adult-like stage that is not yet sexually mature.
In animals, a set of morphological and developmental traits that are integrated into a functional whole -- the living animal.
Symmetry in which the body is shaped like a pie or flowerpot (lacking distinct left and right sides) and can be divided into mirror image halves by any plane through its central axis.
Symmetry in which a central longitudinal plane divides the body into two equal but opposite halves.
Bottom, or underside
Rear, or tail end
Front, or head
An evolutionary trend toward the concentration of sensory equipment at the anterior end of the body.
The outermost of the three primary germ layers in animal embryos; gives rise to the nervous system, epidermis, lens, epithelial tissue of one's oral & nasal cavities, and glands.
The innermost of the three primary germ layers in animal embryos; lines the archenteron and gives rise to the epithelium of the digestive & respiratory tracts.
The endoderm-lined cavity, formed during gastrulation, that develops into the digestive tract of an animal.
Having two germ layers.
The middle primary germ layer in an animal embryo; develops into the inner organs, muscles, cartilage, bone, and blood.
Having three germ layers.
A fluid or air-filled space between the digestive tract and the body wall.
A body cavity lined by tissue derived only from mesoderm.
Animals that possess true coelom.
Fluid filled mesoderm. Ex: Nematoda (roundworm)
Solid mesoderm; no body cavity. Ex: Platyhelmenthies (flatworm)
In animals, a developmental mode distinguished by the development of the mouth from the blastopore; often also characterized by spiral cleavage and by the body cavity forming when solid masses of mesoderm split.
In animals, a developmental mode distinguished by the development of the anus from the blastopore; often also characterized by radial cleavage and by the body cavity forming as outpockets of mesodermal tissue.
A form of determinate cleavage; the cells of each tier sit in the grooves between cells of adjacent tiers.
A type of embryonic development in protostomes that rigidly casts the developmental fate of each embryonic cell very early.
A form of indeterminate cleavage; the tiers of the cells are aligned one above the other.
A type of embryonic development in deuterostomes in which each cell produced by earl cleavage division retains the capacity to develop into a complete embryo.
In a gastrula, the opening of the archenteron that typically develops into the anus in deuterostomes and the mouth in protostomes.
An animal without a backbone (95% of all animals)
Sperm and egg
Embryo with 16 - 64 cells.
Embryo with 100 cells. At seven days, it is a hollow ball of cells that implants in the uterine lining endometrium.
A dividing, growing cell (right after zygote)
The embryo at 2 weeks.
Outer part of blastocyst; forms placenta.
Makes the cells determinate; turns on the cell's direction.
Dorsal Blastiporal Lip
Open cavity during gastrulation.
SSP: Arthropoda, Mollusca, Annelida; RED: Chordata, Echinodermata
Jellyfish; no body cavity.
Sponges; lack true tissue; no body cavity.
One group of cells influences development of another group of cells.
The part of the eye that eventually becomes the retina.
The part of the eye that eventually becomes the lens and the cornea.
Connect to organism, but are not part of it.
Second layer in egg; protect embryo from gases/other
Contains nutrients in an egg.
Collects waste in an egg.
Provides protein for growth in an egg.
Serves as a shock absorber in an egg.
The initial fusion of the sperm to the egg; enzymes digest a hole in the egg's vitelline layer and the sperm fuses with the plasma membrane.
Triggered by the Acrosomal Reaction; calcium is released in the cytoplasm, causing a change in the cortical granules. The sperm fuses with the plasma membrane and fertilizes the envelope. The Cortical Reaction prevents polyspermy.