In Campbell, Chapter 47, esp. pg. 940-950.

Early development

Morula- a solid ball of cells. Basically, after the 8 cell stage a developing embryo can be called a morula.

Blastula- after a number of further divisions, the morula reorganizes itself into a hollow ball, now called a blastula. This process is called Blastulation.

Gastrula- eventually, one side of a blastula will be pulled in towards the center of the ball of cells. This process is called Gastrulation.

 

 

Holoblastic cleavage: complete division of egg (with little or no yolk) Starfish , even Frog

 

Sea urchin gastrulation (47.9)

Frog gastrulation (47.10)

 

Meroblastic cleavage: incomplete division of egg (with a yolk-rich egg) many Fish, Reptiles and Birds.

 

Chicken gastrulation (47.12)

Organogenesis: (47.11)

Ectoderm:

Neural Groove- After many more divisions a line will appear on the outside of the gastrula parallel to the gut.

Neural Fold- the tissue on each side of the neural groove will grow and fold upwards.

Neural tube- eventually the two edges of the neural folds will meet, joining to form the neural tube (the dorsal hollow nerve cord)

Mesoderm:

Somites- blocks of mesoderm that will give rise to bone, muscle and connective tissue.

Table 47.1- Layers from which different organs and tissue are derived.

Chick development:

As you look through the stages of chick development you will see the more advanced stages of organogenesis.

Extraembryonic membranes: (47.14)

Chorion- Outermost layer a protective structure. It helps regulate water loss and gas exchange. Fluid filled

Allantois- often a waste storage or elimination structure. Becomes fluid filled as it fills with waste.

Amnion- a fluid filled sac designed to protect the embryo from shocks and impact.

Yolk Sack- the membrane that surrounds the yolk.