PARASITES OF SIMULIUM LARVAE 85 
which cover the nervous system (fig. 4). The sexual organs 
were never found and it is probable that they had been parasitised 
and destroyed. I saw no signs of the epithelial cells of the in- 
testine, spinning glands or Malpighian tubules suffering, neither 
did it appear that the muscles were ever affected. Under a 
higher magnification the cysts were seen to consist of a grandular 
cytoplasm containing small, irregularly distributed masses of chro- 
matic material (fig. 5). In some young cysts there were vacuoles, 
but these were only detected in living specimens. In other fresh 
material there seemed to be a distinct ectosare layer of a per- 
fectly clear fluid. Otherwise the contents of the cyst seemed to 
be quite homogeneous and to consist of a granular protoplasm. 
On treating with osmic acid this turned a deep brown, indicating 
the presence of fat. By the end of November I noticed that 
the protoplasm was beginning to collect around the chromatic 
masses and the cell contents were divided up into many multi- 
nucleate irregular bodies (pl. 5, fig. 6). During December these 
bodies split into uninuclear, nearly globular bodies (fig. 7). If 
a cyst was then dissected and allowed to float in a drop of water 
it soon burst, liberating countless numbers of these minute glob- 
ules. After they had been liberated about a quarter of an hour 
they began to move independently. Soon they became very 
active, though their power of locomotion was very slight, for 
they did not move their relative position appreciably but darted 
back and forth over a limited area. Each was provided with a 
flagellum. The actual movement could not be accurately ob- 
served as all motion ceased as soon as the specimens were placed 
under a cover glass in a cell slide. I sent prepared specimens 
of these parasites to. Professor Calkins who very kindly replied 
that they probably belonged to the order Gregarinida. I .have 
not, however, sufficient stages to be certain of this, but if this 
be the case there are one or two characters which are not quite 
in accordance with those usually connected with Gregarinida. 
In the first place it is evident that this parasite increases by 
schizogeny in its early stages, for in every host in which it was 
found the number of cysts present was estimated to be between 
500 and 1000 or in some cases more, while surrounding larvae 
