252 Tale Morgan 
spindle of the female egg contained twelve equal chromosomes. 
The somatic cells of the female also contain twelve chromosomes. 
These embryos become sexual females (Plate I, Fig. 1); each 
carrying a single egg. Before the sexual or winter egg is laid its 
polar spindle is produced. One clear case that I. found showed 
six chromosomes. Evidently the expected reduction has occurred 
which from analogy must lead to the extrusion of two polar bodies. 
In the aphids, in fact, two polar bodies have been found by Bloch- 
man and later by Stevens, to be extruded from the winter egg. 
After the polar body formation, the egg should contain six uni- 
valent elements—the same number contributed by the male. 
Hence the fertilized winter egg will contain twelve chromosomes, 
corresponding to the number found in the parthenogenetic eggs. 
With the preceding facts as a basis, we can sum up the chromo- 
somal history of P. fallax as follows, beginning with the spermato- 
zoon. 
The functional spermatozoon contains two accessory or sex 
chromosomes and four others. ‘The unfertilized sexual egg con- 
tains likewise two chromosomes, the homologues of the accessory 
chromosomes, and four others. The fertilized eggs contain, there- 
fore, four accessory chromosomes and eight others. Consequently 
the stem-mother contains these twelve chromosomes, all of which 
appear in the polar spindle of her egg. One polar body is extruded, 
all twelve chromosomes dividing, twelve go out and twelve remain 
in the eggs. The eggs are destined to become female-producing 
and male-producing individuals; both sets of individuals, as well as 
their ripe eggs containing twelve chromosomes. ‘The female 
eggs are larger than the male eggs. [ach gives off a single polar 
body. In the female all twelve chromosomes presumably divide 
equally—twelve going out, twelve remaining in the egg. In the 
male egg, on the contrary, two of the accessories are presumably 
given off with the polar body, ten chromosomes remaining in the 
egg. ‘The two entire chromosomes given off at this time must be 
the partners of the accessories; hence we can understand how in the 
male two of the chromosomes have no partners, and therefore can- 
not pair during synapsis. ‘They pass over in the first division to 
one pole at the time when the other paired chromosomes separate. 
