MOSAIC THOERY -
It was given by W. Roux.
He studied the development of frog's egg. He destroyed one cells by a hot needle out of 2-cells formed as a result of first cleavage. He observed that the remaining cell formed only half of the embryo.
On the basis of the above experiment, he derived a conclusion that the fate of various parts of the egg is predecided.
He further explained that these substances of the eggs remain undifferentiated before fertilization.
The fertilizaton causes reorientation of these substances & the cleavage separates these substances.