my longer — 
1897 | NOTES ON UROGLENA AMERICANA CALK 107 
communication with the center of the colony. Instead, he finds 
that the interior of the ccenobium is filled with a system of 
dichotomously branched threads, which radiate in all directions 
from a common center, and near the periphery unite as a single 
filament with the base of the individual cell. 
Coming to the condition of things in U. Americana, there can 
be no doubt that such an arrangement of threads does not exist. 
In fact, no prolongation of the individual cell is found in any 
form. Careful staining with alum hematoxylin (the method 
used by Zacharias) failed to reveal the slightest trace of any 
connection of the cells with the interior of the colony, and 
various other methods were tried with the same negative result. 
In addition to the test of the stains, the manner in which the 
colony breaks up would indicate that there is no ‘central bind- 
ing structure,” for U. Americana is characterized by the extreme 
delicacy of its colonies, and while other species will stand a 
reasonable amount of manipulation, this form begins to separate 
upon the slightest change of condition, and certainly does not 
assume the definite arrangement of U. radiata, for example. 
Finally, the fact that numerous protozoa swim here and there in 
the ccenobium without obstruction, and colonies half the size of 
the enclosing one are found revolving freely within, would seem 
to show conclusively that no network of threads, as described 
by Zacharias in U. volvox, could exist in this species. 
THE INDIVIDUAL CELL. 
The individual cells, which are placed in the periphery of the 
jelly like globe, vary slightly in size, ranging from 7~I1p in 
diameter. The great majority are spherical, but occasionally 
the end towards the center of the colony will be slightly taper- 
ing. In no case, however, do they approach the long drawn out 
| ee of those cells figured by Ehrenberg and Zacharias, 
Americana is most oe defined es the x ie Bk out- 
| ran - its individual cells. 
Each cell is. provided wie two ei of ‘unequal length, the ae 
reaching Sass the shorter selde om mo ‘than 
