PARASITES OF SIMULIUM LARVAE 81 
entire meront period, at the end of which the myxosporidium 
has grown to a very great size and consists of a multinucleate 
protoplasmic mass measuring up to 2 to 3 mm. in length. Each 
nucleus in the center of the myxosporidium now collects around 
itself a small mass of protoplasm, which becomes somewhat denser 
and is finally enveloped by a membrane, thus forming a globular 
unincleate sporont as previously described. This action spreads 
from the center outwards until the whole myxosporidium has 
been converted into sporonts, although by this time those in 
the center have been already transformed into spores. 
When several myxosporidia are present in one host they all 
remain small so that they together occupy only as much space 
as a single fully developed myxosporidium. The reduction in 
size does not, however, interfere with development, for the small 
trophozoites begin to sporulate at the same time as do those which 
are fully grown. It seems, moreover, that the life history of 
the parasite closely coincides with that of its host, for in every 
case where sporulation was nearly complete, its host was full 
grown and the surrounding larvae from the same batch of eggs 
were pupating. In northern latitudes Simuliidae pass the winter 
in the larval stage and at about the end of October development 
practically ceases. It appears that the parasites in such larvae 
likewise cease to develop, for in all infected larvae collected dur- 
ing November and December the parasites were in precisely 
the same condition of development. This cessation of sporula- 
tion during the winter was noticed also by Cohn (’96) in a species 
of Myxidium. 
THE EFFECTS OF THE PARASITE ON THE HOST 
I was not able to find that any organs except the fat body are 
attacked by these parasites. The musculature, spinning glands, 
and epithelial cells of the alimentary tract showed no signs of 
infection. I have not, however, been able to find the reproduc- 
tive organs in any parasitised larvae. These are always small, 
but can as a rule be found in a good series of sections from a 
healthy larva. When the parasite, however, is present no trace 
of these organs can be seen. 
JOURNAL OF MORPHOLOGY, VOL. 24, NO. 1 
