272 FRANZ SCHRADER 
somes, which are found during maturation and fertilization. 
These then appear as single chromosomes, but betray their com- 
pound character later when they break up into the component 
units again. In view of this fact, I traced out the behavior of 
the chromosomes in the present case with some care. 
In the fertilized egg with itstwenty-two chromosomes, the first 
segmentation division is followed by others which are perfectly 
regular. The first nuclei, still situated in the interior of the egg, 
all show twenty-two chromosomes. After the formation of 
about twelve such nuclei, these approach the periphery, and 
further divisions there establish the blastula. In these early 
stages, and up to the late blastula, division of all the cells occurs 
at practically the same time. In favorable preparations, there- 
fore, the chromosomes in a great many cells of an embryo can 
be counted. One of my preparations shows such a condition, 
and the number can be made out definitely as twenty-two in 
some cases, and at least closely estimated to be such in many 
other cells. This constancy in the number of chromosomes in 
any single embryo is found also in the gastrula stage, where, 
however, divisions do not occur so rhythmically and the cells 
are smaller. Finally, pupae representing the various instars 
frequently show a number of cells in which the chromosomes are 
countable, and if twenty-two chomosomes are seen in one cell, 
every other cell in which the chromosome number can be made 
out will show the same number. Older pupae, that is, those in 
the fourth and latter part of the third instar, having the gonad 
in an advanced stage of development, always prove to be females 
in such cases, as an examination of the reproductive organs will 
show. I have never been able to make an absolutely certain 
count of the oogonial chromosomes, although very good estimates 
can be made in some cases. The number is here also twenty-two 
to all probability—certainly more than eleven. 
The unfertilized egg, like that which has been fertilized, shows 
no irregularities following the maturation divisions and the 
smaller number of chromosomes makes their counting easier. 
As before, after the first few divisions, which here show eleven 
chromosomes, the nuclei travel to the periphery and the blastula 
