676 Blackman .— The Primitive Algae 
saccus , which seems beyond doubt to connect up these green 
Flagellates in a direct line with the Confervales. Chlorosaccus 
(Fig. 14,0) has a superficial resemblance to Tetraspora , but 
is of a yellow-green colour and grows submerged, and attached 
to water-plants, forming irregular hollow mucilaginous spheres. 
The individual cells in the mucilage are pear-shaped, with 
the smaller end outwards, and when division is rapid they are 
found grouped in fours, but this arrangement is soon obscured. 
The chromatophores are parietal disks, several in number, 
and they give the blue colour with hydrochloric acid. There 
are no pyrenoids. When the cells are alive there appears to 
be no cell-wall within the mucilage, but after death a shell 
of wall can be made out which is thick at the superficial small 
end and very thin at the big central end, or even incomplete 
so that it may spring off the dead protoplast (Fig. 14, b) 1 . 
This structure is of great interest as a transition between the 
unwalled Flagellate type and the walled vegetal type, and 
its greater density at the exposed end agrees with a priori 
considerations. Staining shows that the wall is of a pectic 
nature, as in Conferva , and no cellulose reactions can be 
detected. 
The cell-division takes place parallel to the long axis of 
the individual cells which is a Flagellate character, and four 
daughter-cells arise nearly simultaneously. Individual cells 
may enlarge to form resting akinetes with thick walls, and 
these drop out of the colony. 
The greater part of the existence is thus non-motile, but 
zoospore-formation takes place under suitable conditions. 
The zoospores, at first pear-shaped, escape through the 
mucilage, and when free their naked mass contracts to a 
rounder form. Each has two lateral discoid yellow-green 
chloroplasts, and doubtfully an eye-spot. At the fore end 
are two cilia, one three times the body-length, projecting 
forwards, and the other less than the body-length, thin and 
bent. If the zoospore be killed with iodine (Fig. 14,0), both 
PilidiocystiSy Bohlin (’97 c) has a somewhat similar wall. 
