44 E. H. STRICKLAND 
records of their occurrence in North America, they are, at least 
in the locality above named, extremely abundant and readily 
visible to the most casual observer. It would seem, therefore, 
that these parasites, most of which belong to the order Myxo- 
sporidia of the Sporozoa, cannot be generally distributed through- 
out the United States, since there are no previous records of 
their occurrence, although Simulium larvae have, in many sec- 
tions, received very careful attention. The only works which 
have been published in this country dealing with the Myxospor- 
idia are those of Gurley (’93 and ’94), who gave very complete 
accounts of all the forms then known to occur in fishes. Nothing 
however has been written in connection with the Myxosporidian 
parasites of insects. For this reason I have deemed it advisable, 
before describing in detail the species found as parasites of 
Simulium, larvae, to give a brief review of the order Myxo- 
sporidia paying especial attention to the suborder Cryptocystes, 
or Microsporida. From the observations I have made regarding 
the Protozoa and their effects upon Simulium larvae I have no 
reason to doubt that their presence is always fatal to their host, 
and, since in some cases as many as 80 per cent of the larvae are 
parasitised, it is probable that the inhabitants of this part of 
New England owe, to a large extent, their comparative freedom 
from annoyance by these noxious flies to the abundance of their 
parasites. 
I wish to express my sincere thanks to Prof. W. M. Wheeler, 
under whose directions this paper was prepared, both for his 
help and advice during its preparation, and for a critical exam- 
ination of the manuscript. 
NOTES ON SIMULIUM LARVAE IN THE VICINITY OF BOSTON 
The streams in this locality, though usually small, flow rapidly 
over rocky beds, and are thus eminently suited to the require- 
ments of the early stages of the various species of Simulium. 
During the spring of 1911 these streams were found to contain 
immense numbers of the larvae, the most abundant species being 
S. hirtipes, which occurred in such vast masses that in certain 
streams hardly a stone could be found which did not support 
