| The flower-head consists of a set of petals arranged in radial symmetry around a cluster of stamens, and the flower-head is carried on a stalk which bears a set of leaves. |
| At this stage, the blastula is in the form of a hollow sphere with radial symmetry. |
| If you were to watch an embryonic starfish develop, you would see that it begins life bilaterally, but switches to radial symmetry as it matures. |
| At first they are bilaterally symmetrical, their radial symmetry being acquired later. |
| They have not, as is usually supposed, secondarily acquired their radial symmetry. |
| This shows that they evolved from normal ancestors and only secondarily reverted to radial symmetry. |
