50 
Peoria station across the river from the hospital. These were 
not in the deeper or wider parts of the creek, but in its very small¬ 
est lateral divisions and the shallowest margins of the riffles. All 
the specimens taken at this time in these streams proved to be 
Siniulium vittatum. A thoro search of the river margin at Peoria, 
made August 31, was without result, no trace of Simulium being 
found in the main stream. Not a single winged black-fly could be 
found here, altho the presence of small numbers of the pup;e 
showed that a very few might be abroad. The probability of any 
activity of black-flies in conveying pellagra at this place and time 
seems, consequently, very small. 
I have next to scan my miscellaneous data with reference to 
the possibility of distinguishing successive generations, and periods 
of greatest abundance, of the insects on the wing. Throwing all 
these data together I find that we have made collections of adults 
upon thirty-six of the two hundred and four days from April 3 to 
October 24, and that there are two rather conspicuous blanks in 
the series, one extending from May 22 to June 14, 22 days, and 
the other from July 21 to August 11, 20 days. Accepting these 
as indications of the dividing lines between successive generations, 
we may conclude provisionally that we have three generations in 
the season, the first covering April and the greater part of May, 
the second the latter part of June and most of July, and the third 
extending from the middle of August to the last of October. These 
intervals might perhaps be filled in, at least in part, if we had 
larger collections; but they correspond fairly well to such definite 
facts as we have concerning the length of a generation period in 
Sivialiuni. Precise work on this subject has been done only in 
New York, and there only for two species, pictipes and venustum, 
the first of which possibly does not occur in Illinois. For both 
these New York species it has been shown that in the warmer part 
of the summer the development of a generation requires about 
eight weeks, one of which is passed in the egg, four in the larva, 
and three in the pupa stage. Making reasonable allowance for a 
prolongation of the period of development of the earliest and lat¬ 
est generations grown in the cooler weather of the season, we may 
fairly suppose that we have three generations of six of our Illinois 
species, the first extending thru April and May, the second com¬ 
ing in June and July, and the third in August, September, and 
October. Entomologists will readily understand that with any 
such succession of generations as this in a single season, the periods 
of the later ones are always the longer. The other three Illinois 
species seem to give us but one generation each, which we know 
to appear in April and May. 
