70 
B. Millard Griffiths 
primary constriction of the tube and the thin transverse wall dividing 
the lower constriction-segment into two cells. 
In Fig. 18 is seen a slightly different type of division in which 
the constriction is partial and the division has been completed by 
the formation of a transverse wall of considerable thickness. The 
segment of the initial tube thus cut off is about to be divided by a 
thin transverse wall whose rudiment can be seen on the left-hand 
side. The resultant bicellular thallus will have at least one end 
truncated when the thick transverse wall splits and sets it free. 
In Fig. 19 is seen a group of three pairs of cells which have been 
formed by a process of complete constriction into segments, followed 
by the division of each segment into two cells by the formation of 
thin transverse walls. 
One case was observed of what may be a type of asexual repro¬ 
duction (Fig. 20). One of the cells of the common pyriform or ellip¬ 
soidal type appears to be discharging four reproductive bodies 
through a small lateral pore, but the bodies are not of regular form, 
nor do they appear to be motile. Although careful search was made, 
no other example was seen. 
Each cell of the thallus contains one rather large nucleus. It is pro¬ 
vided with a conspicuous nucleolus, and generally lies close to the thin 
transverse wall. The chloroplasts are small and numerous, more or less 
oval in shape, and they frequently contain a small pyrenoid (Fig. 7 
shows nuclei and chloroplasts; nuclei are also shown in other figures). 
The systematic position of the alga is very difficult to determine 
without a further knowledge of its life-history. It is apparently a 
reduced member of a filamentous group but beyond that little more 
can be said with certainty. The only alga showing the least resem¬ 
blance is one brought to my attention by Prof. Fritch, namely 
Peniococcus Nyanzce Woloszynska, an alga from the plankton of the 
Victoria Nyanza (see Woloszynska in Hedwigia, Band 55, Heft. 4-5, 
p. 205, 1914; Zellpflanzen Ostafrikas, 1910; Studien u. d. Phytopl. des 
Viktoriasees, Taf. 7, Fig. 14). It is a thin-walled unicellular alga 
described as “ cylindrices, irregulariter emarginatis, medio con- 
strictis; pyrenoide singulo. Membrana hyalina. Chlorophoris multis. 
Propagatio divisione transversa/’ In the dividing stage it bears some 
resemblance to Tetraedroides forms as seen in Figs. 1, 2, 3 and 7, but 
there is no trace of incipient thread formation and the bicellular state 
is a phase of division and not a permanent condition of the thallus. 
The division of Tetraedroides by complete or partial constriction 
may be a modification of the septation method seen in the Siphono- 
