322 DR. Е. E. FRITSCH ON FRESHWATER АТСА 
D. Systematic EXUMERATION or FRESHWATER ALGE FROM THE 
SOUTH ORKNEYs., 
ISOKONT.E. 
CHLAMYDOMONADACE.E. 
І. ОНтАМУРОМОХАЗ CAUDATA, Wille, Algol. Not. xi. in Nyt Mag. f. Natur- 
videnskab, xli. 1903, pp. 115-118 & 135-136, pl. 3. figs. 4-11. (PI. 10. 
figs. 35-40.) 
Samples 10 and 11, abundant ; also as a rare form in the yellow snow. 
This and the following species are the only forms found in the South 
Orkneys that were obviously preserved in an active motile condition. The 
prominent features of this species, as deseribed by Wille, are the protrusion 
of the posterior end of the individual into a conical tip (figs. 37, 38), which is 
often somewhat bent to one side (fig. 36), the fact that the two cilia are about 
equal in length to the body of the cell and that the strongly thickened base 
of the chloroplast contains a median rounded pyrenoid (figs. 37, 38). There 
can be no doubt that the individuals observed belong to this species, although 
one or two minor points of difference were noted. The cilia were frequently 
found to be as much as 11 times the length of the cell (not shown in the 
figures) ; they were nearly always curved back or spread out at right angles 
to the body of the cell (figs. 37, 38), as Wille shows them. The size of the 
ordinary individuals varies considerably ; length= 13-20 и, breadth = 7-10 h, 
but some of the dividing individuals are much larger. The pointed posterior 
end, as a general rule, lies in the same straight line as the axis of the 
individual, but bending was not uncommon. The cell-membrane is almost 
invariably much more prominently thickened at the pointed posterior end, 
and not uncommonly individuals are found in which the whole of the pointed 
portion consists of solid membrane (fig. 39). In many cases (ef. Wille, loc. 
cit.) the posterior part of the protoplasmic contents is also pointed and in the 
living individual probably in direct contact with the pointed cell-wall, 
although in preserved material generally separated from it by a space 
(cf. however, fig. 38). In a good many individuals, however, the back end 
of the protoplasmic body was rounded off and separated by a considerable 
interval from the pointed tip ; it seems that this may be а preliminary to 
cell-division, as all dividing individuals were found to have the protoplast 
rounded off in this way (cf. fig. 35). Many examples of division (from the 
presence of two pyrenoids in the cell up to the formation of two daughter- 
individuals, fig. 35) were observed ; in all cases such divisions were 
longitudinal and took place after withdrawal of the cilia. Very curious 
division-stages were found in the form of very large individuals (in this ease 
