Development of the ascidian Phallusia mammillata
(Scanning Electron Microscopy).

The egg of the ascidian Phallusia mammillata before fertilization.

The vegetal /contraction pole 10 minutes after fertilization
 3 microvillated surface regions can be distinguished.


Fertilization triggers a microfilament-driven contraction.
The contraction starts from the animal hemisphere and progresses towards the vegetal hemisphere

First cleavage 45 minutes after fertilization.
Cleavage takes place along the animal- vegetal axis
Fertilized egg 5 minutes after sperm entry.
A protrusion called the vegetal/contraction pole has formed as a result of the contraction
16 cell stage.
 Two smaller blastomeres are produced in the vegetal posterior region
Note the specialized region on the small posterior blastomere corresponding to the region of the centrosome attracting body (CAB)

Fertilized egg 5 minutes after sperm entry.
The first polar body has been emitted (on top) and the vegetal/contraction pole has formed (bottom).
32 cell stage
It is seen from the vegetal / dorsal pole of the embryo. The posterior pole is in the left bottom corner.



64 cell stage.
The posterior pole is in the left bottom corner.

110 cell stage seen from the vegetal pole.
The posterior pole is in the left bottom corner.
110 cell stage seen from the animal pole.
The posterior pole is in the right bottom corner
Gastrulation seen from the vegetal pole.
It begins 3 hours after fertilization. The posterior pole is in the left bottom corner.
Neurula
Seen from the ventral region 5 hours after fertilization.
Late neurula seen from the dorsal region.
Young tadpole 7 hours after fertilization.
Tadpole 10 hours after fertilization.