In the Ooplasm of egg of Amphioxus, four regions are quite well marked. Near the vegetal pole there is found very volky cytoplasm. The animal hemisphere of the egg consists of less yolky and transparent cytoplasm.
Around the equator of egg there is a basophilic area in crescent shape at the posterior side, together with another ill-distinct cytoplasmic crescent around the anterior side. Fate map studies have shown that these four Ooplasmic areas have distinct destinies.
The clear cytoplasm which is released from the germinal vesicle during maturation division and occupies animal pole develops mainly into skin epidermis. The granular, yolky cytoplasm which takes up the region around the vegetal pole develops into the lining of alimentary canal.
The crescent of basophilic cytoplasm of posterior side develops into muscles and the lining of the body cavity and thus represents a mesodermal area. On the opposite side of mesodermal crescent occurs a notochord crescent and above the notochord crescent occurs a crescent area which develops into nervous system.
ADVERTISEMENTS:
The fate map of amphioxus thus displays close similarity with that of ascidians and amphibians.