24 
Proceedings of the Royal Society of Edinburgh. [Sess. 
place, the appearance of the cells is somewhat transparent and grey- 
coloured. Not the slightest evidence was obtained to show that it was 
other than homogeneous. In most cases, however (figs. 5, 13, 24), especially 
when the water was examined immediately after it had been collected, 
all stages in the formation of conidia could be seen, and the beginning of 
this formation is marked, as will be explained later, by the appearance 
of a number of large dark dots (figs. 5, 11) which really represent very 
slight protuberances from the surface of the organism, and at first give 
one the impression that they are cell contents. 
The Spiral Twisting of the Individuals. 
The most characteristic feature of this organism is that the individuals, 
at a very early stage, begin to twist. This phenomenon must be regarded 
as a spontaneous vital movement, similar, for example, to the amoeboid 
movement of zoospores of the Myxomycetes. It does not appear to be 
influenced by any external factors ; it is universally found, except in the 
very young stages, i.e. stages immediately subsequent to germination. 
Examples of stages in which twisting has not begun are shown in figs. 
12, 14. In fig. 14 is shown the youngest condition in which the twisting 
is observable. Others, showing a slightly older condition, are shown in 
figs. 15, 16, 17. At this period the individual has no deposit of iron on 
its surface, and in consequence is grey and transparent. Also, although 
the edge is thickened, it is not very pronounced, and would thus present 
no hindrance to the operation. That the period of twisting can be 
prolonged beyond this condition is seen in fig. 18, in which the twisting 
is only just commencing. This condition, however, is far less common than 
the one just mentioned, and it may be accepted that twisting begins almost 
immediately after germination and before deposition of iron has taken 
place. One curious instance of a case in which twisting had been 
dispensed with was seen, which had grown to a comparatively large 
size. In this, however, there was also an absence of deposition of iron 
and an absence of conidia formation, so that very probably the individual 
was not in a healthy condition. When once begun, the twisting goes on, 
until the whole length has been traversed. It does not always take place 
in the same direction, for there may be two or three twists to the right, 
followed by one or two to the left. Thus in fig. 1 there is one right and 
one left twist. In this paper I regard a right twist as one of the same 
kind as in a coil of wire round a stick in which the wire on the upper 
part of the stick goes to the right, e.g. fig. 22 is a coil to the right, and 
fig. 23 one to the left. On examining the various diagrams, it will be 
