146 PROCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
is summed up in two excellent papers by Hurst, “ The pupal stage 
of Culex ” and “The post-embryonic development of a gnat,” and in 
details given by Miall and Hammond (’92) from Hurst’s unpub¬ 
lished notes. 
Three species of Culex as they occurred at different seasons fur¬ 
nished the material on which this paper is based. C. stimulans and 
C. pipiens were used for the study of the perfect insect, and a small 
midsummer form that was not identified gave me larvae and pupae. 
Comparative notes were made at all stages, but failed to bring out 
appreciable differences between the three forms at any time. The 
genus Culex was used instead of the more important Anopheles, 
because early in the study it became impossible to obtain a suffi¬ 
cient number of specimens of the latter, either larvae or adults. 
However, enough material was available to enable me to compare 
the two genera with respect to many structures and to check the 
descriptions given in the literature dealing exclusively with Ano¬ 
pheles. The specimens of Anopheles at my disposal were repre¬ 
sentatives of the commonest New England species, A. punctipennis . 
Technique. 
The cliitin of the imago of the mosquito is not heavy enough to 
offer especial obstacles to research, except as it interferes with the 
penetration of the killing fluids. This was overcome without injury 
to important structures by cutting off the dorsum of the thorax 
while the insect was immersed in the reagent. Of all killing fluids 
that were tried, Gilson’s mercuric nitrate proved most valuable, and 
in the end was exclusively used. In order to remove air from the 
scales, the mosquito was dipped for a moment in alcohol before it 
was plunged into the warm fluid. I made Gilson’s fluid according 
to the following formula : — 
70 % alcohol 10 parts. 
Distilled water 86 “ 
Corrosive sublimate (crystals) 2 “ 
Glacial acetic acid £ “ 
Nitric acid (80%) 1£ “ 
Dissection is of primary importance in a study of the thoracic and 
abdominal portions of the alimentary canal of the mosquito. But 
