108 BOTANICAL GAZETTE [ FEBRUARY 
4u. At the base of the cilia is found an elliptical or oblong red 
spot, and a well defined nucleus is located near the center of the 
cell. One or two vacuoles of a non-contractile character are 
present, and numerous oil globules distribute themselves through- 
out the individual. There is but one chromatophore, which is 
yellowish green in color. This usually clings close to one side 
of the cell, or may occupy the end towards the circumference of 
the colony. The base of the cell is sometimes filled with oil 
globules, but is generally hyaline. Previous to the observations 
of Zacharias two chromatophores were reported as_ being 
present, but he demonstrated the fact that while in U. volvox the 
chromatophore frequently assumed a spiral arrangement, which 
made it appear divided, there was in reality never but the one 
color body. In U. Americana there is no spiral arrangement 
noted, and little or no difficulty is experienced in making out 
the single chromatophore. When the cells are ready to divide, 
however, there are two chromatophores present, and this may 
_ have caused the error in former observations. 
The division of the individual cell takes place in the follow- 
ing manner. A single cell begins to turn so that the cilia are in 
a plane with the tangent of the sphere, instead of at right 
angles. The chromatophore divides and occupies opposite sides 
of the cell and a new red spot makes its appearance somewhat 
away from the old one, but not necessarily in the place where 
the new cilia are to originate. At the point directly opposite 
that at which the old cilia are located a new pair of cilia are 
formed, and we then have a somewhat larger cell with two 
chromatophores, two red spots, and two sets of cilia at opposite 
sides. All of this takes place before the cell begins to elongate — . 
or divide in any perceptible manner. After the new pair of cilia _ 
is completed the cell begins to lengthen in the direction of its 
cilia, and in a short time an oblong cell, nearky three times as 
long as wide, with a pair ¢ of cilia at ‘each end, is formed. It is 
now that actual - divisi vision begins: to ) take eee es it — . 
