SEX DETERMINATION IN THE WHITE-FLY 279 
hand, every egg is fertilized until the spermatozoa are exhausted, 
the first eggs should all produce females, and after a variable 
period, all eggs should result in males. 
I experienced the same difficulties as Williams in his breeding 
experiments. The small size and peculiar delicacy of the adults 
causes the handling of isolated individuals to result in many 
accidents. As the results in the following table seem to indicate, 
the female can control fertilization, and probably some stimulus 
determines whether spermatozoa are liberated or not whenever 
an egg is laid. 
Order of emergence on successive days 
a 29,107 | 79, 407/59, 160 Biot 1o Phe fll, VBxeH 1d 
b 19 172, 164) 39 5c 7h 
ec! |29 39 
d 32, lo) 19 20) oe 52,207 139,107) 429,80) 40 
e 29 Keg 
f OPA ZO athe el ctla Os List 29119 
1 The mother died on the third day after starting to lay. 
THE MYCETOMA CELLS 
The pseudovitelline or mycetoma cells are easily seen in the 
living pupae as two yellow masses situated just posterior to the 
midline. From five to eight of these cells are taken into each 
egg before laying, but their function is problematical, for they 
never seem to be used in the nutrition of the embryo. Occa- 
sionally a duct evidently connecting the cell mass with the ex- 
terior can be made out in the sections, so that possibly they may 
have a secretory function. Buchner (’18) has called attention to 
these cells as hosts of symbiotic ‘fungi,’ and has traced out their 
history in some detail. ‘ 
As I have mentioned previously, in these cells the number of 
chromosomes is found to be irregular. Generally there are from 
thirty to thirty-five chromosomes, the number being independent 
of the sex of the individual. Such irregularities have often been 
observed in similar cells of other animals, and mitosis without 
