64 THE ESSEX NATURALIST
The palpal tibia bears several apophyses on its under side,
all of them lamellar outgrowths of the cuticle, not extensions of
the fore margin of the tibia. A process of this latter kind (the
carpoblem) occurring in most species of spiders is present, but
on the upper side, as usual. Its tip is just visible on the left
side of the tarsus in Fig. 8. The disposition of the inferior
processes can best be gathered from the figure. Two are small
and black, like tiny oblong slabs longer than wide, set upright
on their longer side ; the rest are straplike, much longer than
wide and of the same colour as the carapace. The largest,
which springs from a point very near the base of the tibia, turn
outwards so far that they are clearly visible from above when
the palps are in their natural resting position.
The dorsum of the abdomen is testaceous in colour and
liberally sprinkled with dots and spots of reddish brown, not
arranged in any pattern.
The legs are normal and concolorous, with only two pairs
of black mobile spines on metatarsus i.
PELOSPHAERA ROTANS LAUTERBORN WITH SOME
REMARKS ON OTHER FREE-SWIMMING SPHERICAL
COLONIES OF MICRO-ORGANISMS
BY D. J. SCOURFIELD, I.S.O., F.L.S., F.R.M.S.
[Read November 29th, 1947]
WHILE examining collections of microscopic organisms from
ponds in Epping Forest I have on several occasions come
across a little free-swimming spherical colony of colourless cells
which appears to be undoubtedly the same as that described by
Lauterborn (1906 and 1916) as Pelosphaera rotans. So far as I
am aware this form has not been previously recorded in this
country, and it may therefore be useful to call attention to some
of its peculiarities.
The numerous closely packed unit cells of which the little
ball is composed are elongated egg-shaped (i.e. conical with
rounded ends) and they radiate from near the centre of the ball
with their broader ends outwards. They are colourless and as a
rule appear structureless. They may all be about the same size,
but in many cases the cells in one part are rather larger than
the others and these usually contain a highly refractile globule,
possibly a spore. Very rarely the cells may contain numerous
minute granules, but there seems to be no trace of food particles
or of a nucleus or of a contractile vesicle. As the whole
colony swims freely and rotates in so doing, the cells, or at any