100 Helicosporidium parasiticum 
possible to detect any nuclear membrane surrounding the clear portion of tbe 
protoplasm. 
In this stage the parasite grows a little, and then divides into two (PL IV, 
figs. 3, 4, 5); the smallness of the parasite makes it very difficult, if not im¬ 
possible, to follow in detail the mode of division. In some cases it appeared 
to me to be an ordinary amitotic division; in other cases on the contrary 
I could see a fairly clear mitosis. The two cells resulting from the division 
are of almost equal size and shape (PL IV, figs. 6, 7, 8 and 9); they are 
now more elongated and their protoplasm becomes more basophile. They grow 
a little, undergo a second division (PL IV, figs. 10, 11 and 12) and give rise 
to a small schizont (or morula) composed of four cells disposed in a tetra¬ 
hedral manner (PL IV, figs. 13 and 14). In a few cases only I have ob¬ 
served all four cells symmetrically arranged quadrantally in one plane 
(Fig. 15). The schizont composed of four merozoites is usually slightly oval 
and measures 4/z by 3 p. These schizonts continue their development in two 
different ways: (1) either by breaking up into four merozoites (PL IV, figs. 
16 and 17) which being set free, divide in their turn, or (2) by undergoing 
a third division (Fig. 18) and giving rise to schizonts composed of eight cells 
or merozoites (PL IV, figs. 19, 20). These schizonts, 4/x in diameter, are 
very basophile, so that ifc is often difficult to differentiate their nuclei. They 
undergo no further division, but break up into eight merozoites (PL IV, 
figs. 21 and 22), measuring T7/z-2/x by lf>t which probably divide again in 
their turn. 
I have not yet observed schizonts composed of more than eight cells. This 
multiplication, which forms an endogenous or schizogonic part of the life- 
cycle of Helicosporidium is very active and always results in the formation of 
an enormous number of unicellular corpuscles scattered throughout the body 
cavity of the host or invading its various tissues. 
3. Formation and structure of the spores. 
After a period of very active schizogonic multiplication the parasite passes 
into the second phase of its life-cycle, namely the formation of spores. The 
merozoite resulting from the schizogony increases slightly in size, becomes 
very basophile, and after two successive divisions (Figs. 23, 24 and 25) forms 
a morula of four cells tetrahedrally disposed. Of these cells, one grows more 
rapidly than the others and the whole morula completely loses its regular 
shape (Figs. 26, 27 and 28). 
We now arrive at a very short phase in the life-cycle of the parasite, in 
which the latter undergoes some changes, the nature of which I was unable 
to follow clearly. However, by a few fragmentary observations and especially 
by the subsequent development, I think I have succeeded in reconstructing 
this missing stage, which I shall consider for the present as being hypothetical. 
Of the four cells which form the morula, one, the fourth, which lies now 
separately on one side and is much larger than the three other cells, finally 
