90 E. H. STRICKLAND 
light on this phenomenon, for it is seen that, In many cases, a 
large percentage of the insects contain parasites that are in 
every case fatal to their host. The. Simuliidae occurring in this 
neighborhood are most abundant in the spring, and it is at this 
season that, parasitism is most effective. The most common 
species is Simulium hirtipes. This is found to be heavily par- 
asitized with species of Myxosporidia (sens. lat.). Sometimes as 
many as 80 per cent of the larvae are found to be greatly dis- 
tended with masses of this white parasite, which in every case 
spells death to its host. Another spring parasite is a Nemathel- 
mith belonging to, or near, the genus Mermis. The presence 
of this, also, is fatal to the Simulium larva in which it lives, and 
by this means some 25 per cent of the larvae in certain streams 
were destroyed during the spring of 1911. Very few Simuliidae 
are to be found in the streams throughout the summer, but in 
the fall the early stages of S. bracteatum are common. The 
hitherto undescribed pupa of this species is of interest in that 
the respiratory filaments are only four-branched, a condition ~ 
previously not recorded from North American species, and only 
twice found elsewhere. ‘Together with these larvae occur a few 
of those of 8. vittatum, and later in the season S$. hirtipes is once 
more in evidence. All of these suffer from Microsporidian par- 
asites, which do not confine their attacks to any one species of 
Simulium larva, but freely parasitise all species present in the 
streams during the season of their occurrence. Three Micro- 
sporidian species have been found, and their later developmental 
stages have been traced with sufficient detail to determine their 
probable taxonomic position. 
Since no accounts of Microsporidia, and their relation to 
insects have been made in this country, it was deemed advisable 
to give a somewhat detailed account of this suborder of the 
Sporozoa. 
The three species described from Simulium larvae are: 
I. Glugea bracteata sp. nov. Pansporoblast octo-sporulate. 
Pansporoblast membrane subpersistent. Spores about 3y x 2.5yn, 
short elliptical, filament about six times the length of the spore. 
II. Glugea fibrata sp. nov. Pansporoblast octosporulate. Pan- 
sporoblast membrane not subpersistent. Spores about 6y x 3.5u 
