110 
W. J. Hodgetts. 
diameter being 10-35/x, the height being 6-13/x. Characteristic of 
the species is the shallow notch or indentation on one side of the 
cell—which, however, is absent in very young individuals—the seta 
arising from the base of the cell, passing upwards through the 
notch, The dichotomously branched seta, however, is the most 
remarkable feature about the alga. It is often as much as 150/x 
long, and is composed of a hyaline gelatinous pectose substance, 
which gives no cellulose reaction and takes up stains only with 
difficulty. At the base, where it is broadest, a distinct lumen can 
frequently be seen with a high power, but it contains no visible 
contents and the long, finely attenuated branches are quite massive, 
as is sometimes the whole seta. Hieronymus mentions that 
occasionally the seta is completely unbranched, but such cases were 
never observed in the Harborne specimens. The number of branches 
in the fully developed seta varies considerably, Hieronymus figures 
as many as 14 in one case, but 4-8 was the usual number observed 
by me, although two very long simple branches are not infrequently 
found. The whole seta is very flexible and can withstand very 
rough treatment without being broken off. 
The origin of the seta in the young individuals was worked 
out by Hieronymus, and his account, as far as could be observed, 
appears to be correct. The zoogonidia, by which the organism is 
propagated, first become attached by their hyaline anterior ends, 
but later settle on one side and then become “amoeboid,” i.e., their 
outlines become somewhat wavy or irregular. The hyaline anterior 
end, after losing the two cilia, then grows out as a slender proto¬ 
plasmic thread which immediately secretes a tubular gelatinous 
wall round itself, the cell itself also taking on a membrane ; the 
protoplasmic thread branches several times dichotomously and 
finally the branches, after attaining their adult size, cease growing, 
the delicate tubular branches becoming filled up with the gelatinous 
substance, while the protoplasmic contents gradually retreats back 
into the cell. The basal part of the seta, as stated above, sometimes 
retains a visible tubular structure and Hieronymus occasionally 
observed protoplasmic remains in the lumen by staining with iodine, 
eosin, etc. Hieronymus also observed occasional individuals—■ 
constituting his forma pleiotriclia —with two or even three or four 
setae arising from a corresponding number of indentations at 
various points round the cell, but so far such cases have not been 
observed in the present material. He explains these by assuming 
that the zoogonidia became attached in various irregular ways so 
