SEX DETERMINATION IN THE WHITE-FLY 285 
(Granata, ’09), and Osmia (Armbruster, 713), the equation divi- 
sion results in two unequal second spermatocytes, only one of 
which forms a functional spermatozoon. In the other, compris- 
ing Vespa (Meves and Duesberg, ’07), Neuroterus (Doncaster, 
07), and Camponotus (Lams, ’08), two equal cells result, both 
of which form functional spermatozoa. The rudimentary sperma- 
atozoon produced in the first group is evidently due to unequal 
division of extranuclear material, for in both groups the divi- 
sion of chromatin appears to be equal and is no doubt truly 
equational. 
- The rotifers almost certainly belong to the groups in which 
parthenogenesis is haploid. Parthenogenetic eggs which give 
rise to other parthenogenetic females give off only one polar 
_body and no reduction takes place. The sexual eggs give off two 
polar bodies and the chromosomes are reduced to the haploid 
number. If fertilized, the diploid number is restored and a fe- 
male is produced; if not, the egg develops into a male with the 
haploid number (Whitney, ’09). Exceptional conditions are 
met with in the spermatogenesis. Whitney (717, ’18) describes 
two kinds of spermatozoa in each male, one being large and mo- 
tile, the other smaller and apparently non-motile, and these are 
present in the ratio of 2 to 1. He believes that both classes of 
spermatozoa contain chromatin, and concludes that the first matu- 
ration division gives rise to two cells, one of which forms the 
smaller spermatozoa without further division, while the other 
divides once more to produce two large motile spermatozoa. 
The latter class thus undergoes two divisions and, although Whit- 
ney does not commit himself definitely on this point, the con- 
clusion once more presents the serious difficulty of two equation 
divisions, since males are haploid to start with. When based 
merely on Whitney’s numerical data, such an explanation is very 
tempting, but no cytological evidence has yet been produced in 
its favor. The need for future study of the spermatogenesis is 
obvious.. Taking Whitney’s evidence as given, it is barely pos- 
sible that the numerical ratio may result from the existence of 
two classes of spermatogonia, equal in numbers, but not neces- 
sarily externally distinguishable, one of which would give rise 
