SEX DETERMINATION IN THE WHITE-FLY 269 
TECHNIQUE 
Adults and all the younger developmental stages can be ob- 
tained without difficulty from a great variety of plants, especially 
from members of the group of Solanaceae. In order to obtain 
eggs for the study of maturation, I found it best to put a number 
of females into a vial containing a small leaf of one of their food 
plants. If previously starved for half an hour, they will readily 
settle on the leaf to feed and lay eggs, which after a little prac- 
tice can then be picked off under a binocular by means of a sharp 
curved needle. 
The eggs were fixed best with Gilson-Carnoy’s fluid (equal 
parts of chloroform, absolute alcohol, and acetic acid, saturated 
with sublimate), their chitinous shell making other agents prac- 
tically valueless. Their diminutive size makes puncturing al- 
most impossible. The spermatogenesis, best studied in pupae 
of the third instar, offers considerable difficulty, arising from the 
smallness of the cells and the clumping of chromosomes. The 
fluids of Flemming and Hermann—used both singly and in con- 
junction with urea—and the fluids of Carazzi, Champy, Bouin, 
and Gilson-Carnoy, sublimate acetic, aleohol acetic—with vari- 
ous modifications of these in respect to dilution and temperature, 
were tried with little success. Giulson’s fluid gave a few good 
preparations, while the Bouin and urea method of Allen was more 
consistent and successful than any of the others. The study of 
fresh material with aceto-carmine offered no advantages. I could 
find no differences in fixation due to the various methods of kill- 
ing. In any case, it is absolutely necessary to make an incision 
close to the gonads, and preferably on both dorsal and ventral 
sides. Unless this is done, penetration of the fixing agent is 
always poor. 
Sections of 6u were found best for the study of the maturation 
phases in the eggs, while sections for the spermatogenesis were 
cut 3u to 5u thick. Hematoxylin without a counterstain proved 
to be the best stain. 
