27 
stand, or by the time which elapses during their transportation 
to the laboratory, and we cannot at present attach very great 
importance to the results which have hitherto been obtained. 
We expect soon to be able to extract gases from water by 
means of an air pump and then we shall be in a position to ob- 
tain results which will not be influenced by the conditions men- 
tioned above, and, provided we shall be able to have collections 
carefully made at Havana, the work can very easily be con- 
tinued and completed here at the University. 
Since early in the summer of 1897 we have made regular 
determinations of dissolved oxygen and of carbon dioxide in 
samples taken from the Illinois River and from Thompson 
and Quiver lakes, but the earlier results are less reliable than 
those obtained during the last six months, and these later results 
are themselves not sufficiently reliable to be made at present 
the basis of any general conclusions. 
Yours very respectfully, 
ArtHuR W. PaLMER, 
Professor of Chemistry. 
REPORT OF THE ENTOMOLOGICAL ASSISTANT. 
To the Director of the Laboratory. 
| Sir: During the season of 1897 I was in the field, prima- 
rily for entomological observation and collection, from June 
29 to August 13, giving attention particularly to the gathering 
of information and material for use in completing our work on 
Odonata and Mollusca. In 1898 two visits to the field were 
made for work on Odonata, Ephemerida, and Mollusca; a week 
in spring, from April 19 to 25, and two weeks in midsummer, 
from June 21 to July 7. 
The accumulations of material and notes were already 
sufficiently large for group studies at the beginning of the two- 
year period covered by this report. Every opportunity has 
been taken to make desirable additions to them, and they now 
stand as a superb basis for the study of any group of aquatic 
forms. The material is all arranged by orders, and consists of 
about 4,250 vials and bottles of specimens. 
There are now in various stages of preparation four papers, 
