INVERTEBRATES OF LAKES GENEVA AND MENDOTA. 
487 
nois in the hottest weather of the year. They usually, if not always, follow upon 
flooding rains, and thus occur when the streams are full or overflowing with turbid 
water loaded with the products of decay. They are sometimes succeeded by great 
deposits of rotting fish along the river front of towns, requiring burial to protect the 
general health. 
We have in the facts reported here abundant material for surmise and the con- 
struction of hypotheses ; but no means of precise verification. Arriving at Lake Men- 
dota after the practical cessation of the epidemic argued a disappearance or a great 
reduction of its cause, and unable to obtain good material enough from which to gen- 
eralize, I have withheld this reimrt in the hope that a similar occurrence within my 
reach might enable me to complete the investigation. Several of the kind have, in 
fact, been noticed in Illinois within recent years, knowledge of which has reached me 
through our State Fish Commission, but always much too late to permit successful 
study. It therefore now seems to me best merely to put on record the facts already 
ascertained, and to postpone discussion until more evidence has been collected. 
