536 THE AMERICAN NATURALIST. | [Vor. XXXIV. 
the large ones come on. The commonest small form to appear 
is A. radiosa — occasionally A. limax (or some similar form). 
I have tried these tub cultures only during the warmer months 
of the year (April 1 to November 1). With rare exceptions they 
are successful. Mussels alone have frequently given me good 
amoebas, but the Nitella and the crayfish increase the chance 
of having enough to start with. The sand may come from 
anywhere, roadside or creek. The water is well water pumped 
into a reservoir tank. I am inclined to believe that a trace of 
mud, got along with the mussels or Nitella, is an advantage. 
But anything more than a trace is, here, sure to result in the 
development of Tubifex, which quickly spreads over the bot- 
tom, strewing it with fæces, while the ameebas, even if they get 
a start, gradually become scarcer, soon disappearing. 
In the succession of organisms developing in such a culture, 
the bacteria are followed by the flagellate, and then by the cili- 
ate Infusoria, both especially abundant in the surface film, where 
they feed upon the zoöglæa. A loose brown growth accumu- 
lates on the bottom, but more thickly on the wall of the tub. 
This consists of many things: fungus, hyphz, bacteria, unicel- 
lular algze, quantities of Infusoria, often Heliozoa (Actinophrys), 
and rotifers. The stuff gradually falls from the wall and accu- 
mulates on the bottom, round the edge. In this * growth ” the 
small amocebas referred to above are often found, and in it .S/ez- 
tor caeruleus frequently develops in the greatest abundance. 
It is usually after this growth has begun to accumulate on the 
bottom, round the edge, that the large amoebas make their 
appearance. They are more abundant over the general surface 
of the sand than in the thick masses of brown stuff. By this 
time the Infusoria are no longer present in excessive numbers. 
The Entomostraca soon develop, and the amcebas gradually dis- 
appear. Ithink Cyclops is particularly destructive — it is con- 
stantly *rooting" in the sand. Frequently, before the arrival 
of the Crustacea, small planarians appear in numbers — Micro- 
stomum lineare has swarmed several times. 
In a culture of this kind (mussels and Nitella both taken 
from a creek, the bottom of which in the particular locality is 
made up of soft mud, with abundant Tubifex), that had been 
