1120 Proceedings of Royal Society of Edinburgh. [sess. 
varies greatly in the different individuals, the narrower ones 
measuring from 4 to 7 /x, the broader ones from 7 '5 to 11 g, but 
no relation seems to exist between the breadth of a cell and its 
length ; there are broad and long, broad and short, narrow and 
long, and also narrow and short individuals ; perhaps the broad 
individuals generally are a little longer than the narrow ones. 
Nor does any clear difference express itself between the broad and 
the narrow ones as regards the length of the setee. But never- 
theless do the broad individuals differ from the narrow ones in 
small morphological characters as well as in the breadth, which 
will he seen if we compare the drawings of some specimens (PI. II. 
figs. 1-5). In the broad specimens an undulation of the cell 
contour near the basis of the setae indicates the place of the seta 
of the neighbour cell, while in the narrow specimens the cell 
contour is not undulated, hut has only a double outline, i.e., the 
cell has a furrow, in which the seta of the neighbour cell fits in. 
Further, the narrow specimens are cylindric, the broad ones are 
applanated; a specimen, which was 11 g broad at the one axis, 
measured only 4 g at the other. Many of the narrow specimens 
are somewhat curved, while the broad ones always are straight. 
By all this I think we must conclude that the broad specimens 
belong to one race or species, the narrow ones to another. 
In all the samples in which Rhizosolenice have been observed, 
some specimens have been measured with regard to the breadth 
of the cell. It was a priori possible that the two races were 
different forms of one season-dimorphic species ; if so, we must have 
found samples in which only one of the forms occurred, other 
samples in which the one form was rare, the other common, etc.,* 
but this does not seem to be the case, as both races were present in 
about the same quantity in the samples in which a larger number 
of specimens has been met with, as will be seen from the following 
text-table II. In the first sample (14th July 1902) I did not succeed 
in finding the broad race, nor did I see more than three individuals 
of the narrow ones. In the samples from the early spring of 1903, 
very few specimens were seen, and the greater part of these were of 
the broad race ; but as the number is so small, I dare not draw any 
conclusions based on observations of as few specimens as these. 
* Cf. Schroter, C. , and Vogler, P. (1901), 
