14
Beyond this point I have observed no further growth, although I have ex-
amined coccidium-infected mosquitos kept alive to the twelfth day. Hence,
I think, the diamensions here given may be considered as the maximum size
reached by these bodies, at any rate in the living host. They are now easily
visible by a magnifying glass, and are therefore nearly visible to the naked eye.
If mosquitos of this stage (or indeed earlier) be dissected in plain water, a
curious phenomenon will be observed when microscope examination is com-
menced at once. The coccidia will be seen bursting in all directions, pouring
out their contents slowly into the surrounding fluid, and leaving behind a
collapsed and wrinkled capsule still attached to the stomach wall. This is pro-
bably due to the difference in specific gravity of the medium in which they now
find themselves, and can be checked by dissection in weak formalin (10 per
cent.), or perhaps in salt solution.
On examining a stomach immersed in formalin with a medium power of
about 300 diameters, the coccidia will be seen everywhere, not only protruded
but often extruded from the tissues, though still attached to them by some in-
isible adhesions. Each coccidium will have the appearance of a little, clear ball
of glass containing numerous brilliant points, the oil-globules previously noted.
Some of them in addition possess a more refractive but ill-defined central core,
which in a few cases I have observed to have the appearance oí being divided
into six or eight portions. These appearances, however, vanish on the imposi-
tion of the cover-glass, after which the coccidia, probably from being slightly
flattened, present only a granular structure as shown in Plate IX. Seen by a
still lower power, the stomach studded with coccidia has the appearance given in
outline in Plate I, figure 23 ; where the mosquito has been re-fed on proteosoma-
infected birds, younger generations of coccidia are seen embedded in the tissues
or just emerging from them.
On applying the oil-immersion lens, the largest coccidia of the sixth and
seventh day are observed to have a structure similar to that of the fifth day
namely, a more or less granular and vacuolated plasma studded with numerous
brilliant points. In many of them, especially after preservation, there is now
however a very marked contraction of the contents within the capsule (Plates
VII and VIII, and Plate I, figures 16, 17 and 21); which, indeed, is to be seen
in preserved specimens of an earlier stage of growth.
I have said that after this point I have witnessed no further growth of the
coccidia, even in mosquitos kept alive to the twelfth day. Hence we may per-
haps expect that they have become ripe for sporulation. No such thing has
however been observed ; and we may therefore conjecture, unless I happened
to have overlooked it, that it may occur either (a) in the living insect after
twelve days, or (b) some time after the insect's death.
Further research is therefore required on this which now becomes the most
important and interesting period of the life-history of the gymnosporidia
because on it depend our chances of future progress. To plunge into hypothesis
for a moment, we may remark that since the mature coccidia find themselves in a
closed cavity, namely, the body cavity of the host, there appears to be no means
by which they can escape from that host during its life to undergo sporulation
in external nature, as is the case with coccidium oviforme, It would appear
then that sporulation should occur either within the living host, as with Eimeria
or within the dead host. The first would point to a completion of the life cycle
by a direct infection of men and birds by the coccidium-spores in the mosquito -