SEX DETERMINATION IN THE WHITE-FLY 283 
If this account be correct, the case presents no difficulties, but 
Schleip states that he could find no such doubling of chromo- 
somes after maturation. He believes that the chromosome num- 
ber observed in the maturation is diploid and that this is kept 
constant because both maturation divisions are equational. 
Such an explanation meets with serious difficulties, arising 
both A priori and from detailed observations on the meiotic phe- 
nomena, especially in case of the Hemiptera and Orthoptera. 
It has been established to a practical certainty that the reduc- 
tion and equation divisions are perfectly definite in their opera- 
tion. <A fine substantiation of this rule is furnished, for instance, 
by Trimerotropis, an Orthopteron in which Miss Carothers (717) 
has described several heteromorphie chromosome pairs, in which 
the synaptic mates differ distinctly inform. No correlation exists 
between the different pairs in regard to their distribution during 
reduction, so that a daughter cell may receive either member of 
such pair as a matter of chance. After separation, each homo- 
logue undergoes an equation division, and there is never a viola- 
tion of this proceeding. A more special case is found in the ‘m’ 
supernumerary of Metapodius (Wilson, ’09) and also the extra 
chromosome of Oenothera lata (Gates, 714). Such supernumer- 
ary chromosomes may divide at either the heterotypic or homo- 
typic division, but they never undergo more than one division. 
Finally might be mentioned the sex chromosomes, which are 
subject to the same rule. Before basing an explanation on the 
grounds of two equation divisions, therefore, a more sufficient 
proof than is given for Rhodites rosae and a few similar cases 
must be presented. 
It is very possible that the problem involves the formation of 
multiple chromosomes. It was this most difficult point in Hy- 
menopteran cytology which lay at the bottom of the long con- 
troversy concerning the bee. Nachtsheim (713), who seems to 
have said the final word in this matter, offers the following ex- 
planation: The diploid number in the bee is 32, but through a 
coupling of these only 16 appear to be present in the oogonia. 
The reduced nucleus presents 8, and these must therefore be con- 
sidered as bivalent. The case is complicated still further by the 
fact that 64 chromosomes appear in some somatic cells. 
