A study of the Chromosomes in three species of Pseudococcus. 
57 
vesicles in the spermatogonia therefore that they differ from typical 
heterochromosomes, and this omission may possibly be attributed to the 
smaller size of the Pseudococcus cell elements as compared with the 
easily observed homologous structures of Orthoptera. With this one ex- 
ception then, the comparison holds point for point. 
The assumption that these massed chromosomes represent or resemble 
sex chromosomes does not entirely explain the reduction however. Some 
explanation must be sought for the fact that there is no haphazard or 
random distribution in that division. It was this consideration that led 
me to postulate in my previous paper (’21) that the ten chromosomes 
are comprised of five pairs, the members of each pair being homologous 
to each other except for one feature. That feature is manifested by an 
earlier condensation of one member of each pair, and the difference brought 
about in this way is sufficient to prevent pairing and consequent tetrad 
formation. On the. other hand this difference is not sufficient to hinder 
the members of each pair from going to opposite poles at reduction just 
as do the m-chromosomes of x\lydus which remain separate all through 
the synaptic period of the autosomes and just barely touch each other 
shortly before the critical division. Each pole in the Pseudococcus reduc- 
tion thus receives five chromosomes. That the massed group of chromo- 
somes always goes to one pole is in tum due to the tendency of its members 
to clump which causes them to act asaunit. The loosely grouped chromo- 
somes then of necessity go to the opposite pole. 
Another solution, which may be only a Substitution of words, is based 
on the behavior of the ordinary X Y chromosomes. If the massed group 
partakes of the nature of the X chroniosome, and the loose group repre- 
sents the Y chromosome, then the reductional distribution is explained. 
It must not be forgotten, however, that the Y chromosome as usually 
observed, shares with the X chromosome the persistent contraction or 
early formation during the prophases, — a feature which is not paralleled 
by the loose group of chromosomes in the present instance. It is apparent 
that any interpretation must needs be of speculative nature and encounters 
the basic difficulty which lies in the fact that we still do not know how 
to explain the early or persistent condensation of heterochromosomes. 
The difficulty of throving much light on this problem through purely 
cytological investigation must be manifest. 
Certain it is, that the exceptional behavior of the Pseudococcus male 
chromosomes can not be entirely explained on the basis that early con- 
densation is alone due to the fact that the five pairs are not tmly mated 
and that therefore one member of each pair is not available for the synaptic 
