56 
Transactions of the Royal Society of South A frica. 
which appear to be referable to Z. pectinatu7n (Fig- 25, D-H). The first 
step appears to consist in a marked thickening of the membrane, the 
thickening sometimes showing some stratification, though this is frequently 
obscure at this stage (Fig. 25, G). At the same time the cell-contents 
become densely crowded with food-bodies which seem in the main to be of 
the nature of oil-globules ; this accumulation may altogether hide the two 
chloroplasts (Fig. 25, G), although in many cases their presence is indicated 
by a separation of the dense cell-contents into two more or less distinct 
halves (Fig. 25, B and H). Subsequently, as the thickening of the 
membrane progresses, the cells become ventricose in the middle (Fig. 25, 
jD and jff) ; the swelling is, however, confined to the central part of the 
cell, the ends having straight parallel margins for some little distance 
(Fig. 25, E, F). At this stage the cells may be more than twice their 
original width in the middle. The septa mostly become especially strongly 
thickened, so that the cell-contents are relegated to the median swollen part 
(Fig. 25, F), although this thickening of the septa may apparently 
commence at a rather later stage than that of the longitudinal walls. 
Ultimately these septa split across the middle (Fig. 25, H) and the akinetes 
become free. Large numbers of such splitting threads and of isolated 
akinetes were encountered in the sediment of Sample 36. The individual 
akinetes either have neatly rounded truncate ends (c/. the upper end in 
Fig. 25, F) or the ends bear remnants of the thickening layers (lower end 
of Fig. 25, F). 
It may be added that all stages between the normal thin-walled Zygnema 
pectinatum filament and such thick-walled threads as are shown in Fig. 25, 
G, were found, and seeing that the diameter of the cell-contents of the latter 
is the same as that of the former, it seems fairly safe to conclude that the 
akinetes are those of this species. 
The following is a synopsis of the dimensions of these akinetes : — 
fi 
/X 
/X 
/X 
fi 
/X 
Width of cells as in Fig. 25, G 
36 
36 
37 
37 
39 
40 
42 
42. 
Length „ ,, „ 
100 
105 
83 
129 
135 
170 
165. 
Thickness of membrane of ditto 
3 
6 
6 
4-5 
2-5 
7-5 
7-5. 
Width of akinete in the middle 
60 
70 
73 
67 
57 
Length of akinete .... 
174 
200 
Thickness of membrane in middle . 
12 
12 
15 
15 
14 
„ „ ,, at the apex . 
60 
66 
Width of apex .... 
30 
30 
2. Zygnema cyanospermum, Cleve, Svenska Zygnem., Nov. Act. Eeg. Soc. 
sc. Upsal., ser. iii, vi, 1868, No. xi, p. 28, PI. VIII, figs. 6-8. 
forma paullo major, cellulis brevioribus, l-3plo longioribus quani latis. 
Lat. cell, veg., 27-30 /x; dimension, zygosp., 42 x 39, 42 x 43, 45 x 42, 
48 X 48, 48 X 33 (elliptical zygospore), 50 x 48 /x. (Fig. 25, A-C.) 
