If we bear these circumstances in mind, we can almost always tell whether an arcella will develop air-vesicles or no; and if it has already developed them, we can tell whether they will increase or diminish.    From Wordnik.com.  [Unconscious Memory] Reference

After from five to twenty minutes, the specific gravity of the arcella is so much lessened that it is lifted by the water with its pseudopodia, and brought up against the upper surface of the water-drop, on which it is able to travel.    From Wordnik.com.  [Unconscious Memory] Reference