SEX DETERMINATION IN THE WHITE-FLY iS 
is formed. The latter, as well as the gastrula and the various 
pupal stages, show perfect constancy in the chromosome num- 
ber. And in this case, finally, the older pupae, which show 
eleven chromosomes in the somatic cells, are found to be males 
with testes partly or fully developed. The only exception to the 
constancy in the number of chromosomes of the various somatic 
cells is furnished-by the pseudovitelline cells or mycetoma, to 
which I will refer later. 
Although I realize fully the danger of laying too much stress on 
chromosome counts of somatic cells, their remarkable constancy 
and definite coincidence with sex in this case cannot be altogether 
without significance. 
SPERMATOGENESIS 
The spermatogenesis presents considerable difficulty, due 
chiefly to the diminutive size of the cells and the tendency of 
the chromosomes to clump. In the hope of finding more favor- 
able material, I also investigated a number of other genera and 
species of Aleyrodidae, comprising the following: Trialeurodes 
coryli, T. packardi, T. morrilli, Tetraleurodes mori, Aleurochiton 
forbesii, and also unidentified species from the common ragweed 
(Ambrosia artemisifolia), wild lettuce (Lactuca canadensis), Vi- 
burnum acerifolium, and Eupatorium purpureum. None of 
these, however, offered better conditions than are to be met 
with in Trialeurodes vaporariorum, and, on the whole, very 
little difference was observed. 
I found it impossible to count the chromosomes in those 
phases which are undoubtedly spermatogonial. However, the 
mitoses are evidently normal. The equatorial plates of the - 
various spermatogonial divisions observed are regular and iden- 
tical in size. 
The main problem of course centers in the question of how the 
haploid number of chromosomes is retained in the male during 
maturation. Asis well known, Hymenoptera, in which partheno- 
genesis is haploid, simply eliminate the reduction. An attempt 
is indeed made to initiate the process, but the chromosomes do 
