How To Study Living Animals


Definitions.

Cleavage stages,

two, four, eight, sixteen cells, etc., arising by repeated division, starting with the egg herunterladen.

Blastula,

a hollow sphere, the wall of which is composed of a single layer of cells.

Gastrula,

a stage formed from the blastula by pushing in one side of the latter, so as to form a more or less cup-shape structure herunterladen.

Observations.

1. Is there any considerable difference between the size of the egg and the size of the blastula and gastrula? Has development taken place by an increase of size or by an increase of complexity microsoft office kostenlos downloaden vollversion deutsch chip?

2. Contrast the blastula and gastrula as to number of cavities, number of cell layers, number of external openings.

3. Suggest protozoans that resemble the egg and blastula respectively. What invertebrates resemble the gastrula in body plan?

Suggested drawings.

a. Some of the cleavage stages.

b. A blastula.

c. A gastrula.