13
If the mosquito has been fed again, say on the night of the second day
(Monday night), the condition of the stomach and of the new crop of eggs (if
present) will be that of the second day already described. If it has been fed
again on a bird infected with proteosoma, as on the bird on which it was origin-
ally fed, the stomach will most probably be found to have on its external coat
a fresh generation oí young pigmented cells, in every way similar to those already
found on the second day. On the margin of Plate VI, one such is figured lying
next to some cells of an older generation. The new cells are evidently derived
from the second feeding.
The two varieties of cells, vacuolated and hyaline, still exist. In both the
pigment is arranged as before, and may still oscillate within a small area ; but
it is greatly reduced in amount, being sometimes reduced to only one or two
granules lying close to a large vacuole and difficult to find. As the cells reach a
major diameter of about 35 μ , namely half the growth which they are destined to
arrive at, the pigment disappears altogether, while the bright refractive points
referred to as beginning to appear on the third day increase in number and per-
haps in size. In the vacuolated variety the number of vacuoles and granules
increases with the growth.
A noteworthy phenomenon manifests itself at about this stage. If the cover»
glass has been placed so lightly on the stomach-tissues as not to crush them,
and if a medium power be used, the pigmented cells will be seen protruded from
all parts of the external wall of the stomach like warts on a finger (in Plate 1,
figure 23, this appearance is given, though the bodies there shown are of later
growth than those now described) ; that is they protrude, not into the cavity of
the stomach, but into the general body cavity, the coelom. This might perhaps
have been inferred from the first position of the cells on the external coat of
the organ.
From this point, then, the parasitic nature of these bodies becomes obvious,
and we may, I think, venture to assume, at any rate provisionally, that they
are coccidia. I will therefore now call them proteosoma-coccidia.
The identity of the cells of over 35 μ in diameter without pigment with
those of under 35 μ with pigment is easily established by the similarity of
structure in other respects. In many cases pigment may still exist in the cocci-
dia which protrude from the tissues ; and there is no possibility of mistake with
regard to the continuity of development»
Fifth day—Thursday.—The coccidia continue to grow, and may reach a
diameter of 50 μ at the end of this day (120 hours). Some of them not
only protrude beyond the tissues, but may be seen to be almost distinct from
them. The difference between vacuolated and hyaline cells is not so marked
as before ; and each coccidium now consists of a capsule containing a more or
less granular and vacuolated substance studded with the numerous small bright
points which I take to be minute oil globules. If the insect has been fed again
on blood containing proteosoma, pigmented coccidia of a younger generation
will generally be found interspersed among the older and non-pigmented ones,
(Plate VII).
Sixth day—Friday—and Later.—At the end of this day the coccidia
arrive at a growth of 6ο μ (144 hours), while some increase still further and may-
reach a size of nearly 70 μ. The largest cells seen by me measured, when
compressed by the over glass, 73 μ. by 62 μ. These coccidia are figured in Plate
VIII after preservation in weak formalin.