Birds and Mammals




Transcript,  Watch Development 12.3

00:00

One day after fertilization, the embryos are observed under the microscope. If fertilization has occurred, a single cell is seen containing two nucleii, male and female.

00:17

Two days after puncture, the embryo divides itself and contains two cells, with one nucleus per cell

00:23

… which in turn starts to divide into an embryo of four cells if its  development is optimal.

00:31

Three days following puncture, the embryo starts to divide and consists of eight cells if its development is optimal.

00:40

On day four the embryo divides a number of times, becoming a morula.

00:49

This is when it begins compact.

00:53

On day five, the embryo contains more than 100 cells. In the center there is a fluid-filled cavity.

1:01

Finally, the blastocyst will shed the membrane that surrounds it. This is called hatching.