86 E. H. STRICKLAND 
of the same generation were free from attack. Secondly, the 
nucleus is not single from the earliest observed stages, but seems 
to occur for the greater part of the organism’s life in the form of 
diffusely scattered chromatic masses. There is, again, usually 
no sharply defined layer of ectoplasm surrounding the endoplasm, 
while in the latter vacuoles are present. Another feature is that 
the presence of this parasite has a marked pathological effect, 
for parasitised larvae have the development of their histoblasts 
arrested (pl. 6, fig. 7) so that they must die at, if not before, 
pupation. Since in the streams in which this parasite is present 
it must kill well over 50 per cent of the somewhat scarce larvae, 
it would seem that it must be an important agent in the reduction 
of Simulium larvae in the neighborhoods where it occurs, and 
for this reason, apart from its scientific interest it would be of 
advantage to ascertain in detail its life history and distribution. 
The host of this Gregarine is the larva Simulium bracteatum. 
It was found infecting about half of the larvae in streams in 
Franklin Park and at Hyde Park near Boston, Massachusetts, 
from October to December. The streams where it occurred had 
not been examined earlier in the year and contained no species 
except S. bracteatum. 
THE ECONOMIC VALUE OF PARASITES OF SIMULIIDAE 
It will be seen from the foregoing notes that there are in the 
neighborhood of Boston three distinct classes of. parasites infect- 
ing, and in each case killing, Simulium species in their larval 
stages. Summarizing my observations for the single year, 1911, 
there are the following: 
1. Parasites of the spring brood of Simulium. 
a. Various Myxosporidia sens. lat., up to 80 per cent mortality 
c. Mermis sp., up to 25 per cent mortality 
If. Parasites of the fall brood of Simulium. 
a. Glugea bracteata, about 10 per cent mortality 
a. Glugea fibrata, about 5 per cent mortality 
a. Glugea multispora, rare 
b. Gregarine species, up to 50 per cent mortality - 
