It is a matter of common observation that the blue of the sky is highly variable.

Similarly the substance we call wine is undeniably variable in composition.

Ordinary observation of the landscape shows that there is another part, highly variable from day to day, and due to suspended matter, much of which is fine enough to scatter light of blue quality.

wide, but is very erratic in outline and variable in thickness.

In this sub-order the characters of the hydranth are very variable, probably owing to the fact that it is exposed and not protected by a hydrotheca,.