Dicranochaete reniformis Hieron. 
111 
that the anterior end, from which the seta develops, was more or 
less overgrown by the rest of the cell, the seta thus growing out 
from some point of the flat basal surface, and at the same time 
forking near its base while growing between this surface and the 
substratum, the ultimate branches emerging at different points 
round the circumference of the cell. This explanation is supported 
by the fact that the individual setae in these cases were usually 
simple or only forked once, at the same time being much shorter 
than the single seta of a normal individual. The same author also 
observed typical individuals which entirely lacked a seta, such 
cases being most frequent in the late summer generations of 
October. The hypothesis that the setae serve as organs of 
protection against the attacks of various small aquatic animals, 
especially Infusoria, seems a priori quite reasonable. 
We now come to the description of the cell-membrane in the 
adult individual. According to Hieronymus the very thin basal 
wall may sometimes give a cellulose reaction with chlor-zinc-iodine 
but prolonged treatment with this reagent failed to give it in the 
present instance. The dome-shaped part of the cell-wall is sharply 
marked off into two regions, the uppermost half being fairly thin and 
characterized by the deep red colour it readily takes on when stained 
with Congo-red, the rest of the wall remaining practically unstained ; 
this dorsal part is also coloured violet with chlor-zinc-iodine and 
undoubtedly consists of cellulose. Hieronymus states that in his 
specimens this partofthe wall possessed minute cone-shaped, pointed, 
cellulose protuberances or tubercles, and these are very conspicuous 
in his figures, sometimes being arranged in two tolerably regular 
concentric circles, forming a sort of crown to the cell. In the 
Harborne material, however, these tubercles could not be found, the 
rounded dorsal part of the wall being always quite smooth even when 
examined under the highest powers ; the absence of these protuber¬ 
ances is the most conspicuous difference between the English 
specimens and those figured by Hieronymus. The difference is 
hardly specific, and indeed Hieronymus states that they were not 
always present; perhaps the smooth form ought to be looked upon 
as a variety—which may be termed var. Icevis —differing from the 
type only in this respect . 1 In individuals stained with Congo-red it 
can easily be seen that the red-stained dorsal part of the wall is 
seated on the protoplast like a sort of cap, and is not continuous 
1 D. reniformis var. Icevis :—superiore parte tuberculis orbata ; caetera ut in 
typo. 
