122 
F. E. Fritsch. 
THE OCCURRENCE OF PLEODORINA IN THE FRESH 
WATER PLANKTON OF CEYLON. 
N 1893 Shaw 1 described an important new genus of Volvocineae, 
which, while closely resembling Eudorina in type of cell and 
colony, showed a marked differentiation between the purely vege¬ 
tative cells and those subserving asexual reproduction (gonidial 
cells); of the spherical colony of 64 or 128 cells the vegetative cells 
constitute about one half, occupying the anterior region, whilst the 
posterior half consists of gonidial cells of 2—3 times the diameter 
of the former. This Alga was described as Pleodorina californica, 
Shaw. Subsequently a further species— P. illinoisensis —was 
described by Kofoid,- in which 32 is the normal number of cells in 
the colony and in which only four vegetative cells are present, the 
remaining gonidial cells being up to twice their diameter. 
Both species have, as far as I am aware, as yet only been found in 
various localities in the United States. 
In the course of a preliminary examination of the Plankton, 
collected from diverse freshwater areas in Ceylon during September 
and October of last year, I met with numerous individuals of 
Pleodorina californica in material from two of the tanks of the 
central low country, viz. from tank Periyakulam near Trincomalie, 
and from Lake Mineri, one of the largest areas of fresh water in 
the island. The colonies consisted of about 64 cells and were 
bounded by a well-defined mucilaginous envelope; the gonidial cells 
were from 15—20 /a in diameter, the vegetative cells from 6—9/x. 
In each of the gonidial cells 3 or more large pyrenoids could be 
detected, whilst in the vegetative cells only one occurred. 
Associated with these typical colonies of Pleodorina two other 
types of colonies were found in both localities. One of these is 
represented by spherical colonies of 32 cells each, which are about 
the size of the gonidia of Pleodorina, the colonies being indistin¬ 
guishable from the vegetative form of Eudorina elegans. The other 
type is represented by colonies of 64 cells each, which are about the 
same size as the vegetative cells of Pleodorina. It is possible that 
these two types represent developmental stages of Pleodorina, the 
64-celled form arising by the division of all the cells of the 32-celled 
1 Pleodorina, a uevv genus of the Volvocineae. Botan. Gazette, 
Vol. XIX., 1894', p. 279—283. PI. XXVII. 
2 Bulletin Illinois State laboratory of Nat. Ilist., Vol. V., p. 
273—293; reprinted in Ann. and Mug. Nat. Hist., Vol. VI., 
Ser. 7. 1900, p 139—156. Plates V. and VI. 
