CHROMOSOMES AND MITOCHONDRIA 265 
and the drones parthenogenetically. The history of 
the chromosomes has here been worked out by 
Nachtsheim (1913). The primary odcyte contains 
sixteen chromosomes in the form of eight tetrads; the 
mature egg and polar bodies are each provided with 
eight chromosomes (Fig. 71, E); the inner half of the 
divided first polar body fuses with the second polar 
body, forming a “‘Richtungskopulationskern” (Fig. 
71, F) which does not give rise to the male germ cells 
as Petrunkewitsch (1901) claimed, but degenerates. 
The cleavage nucleus in the parthenogenetic egg 
which produces the male shows sixteen chromosomes 
which divide to form thirty-two or sixty-four in 
the somatic cells, but do not increase in number in 
the spermatogonia. The first maturation division 
is unequal, and a “‘polar body”’ without any chroma- 
tin is pinched off (Fig. 71, A-C, Rk,). The sperma- 
tids are likewise of two sorts; the smaller (Fig. 71, 
C, Rk.) contain as many chromosomes as the larger 
(16), but degenerate, while the larger transform into 
spermatozoa. The fertilized (female) eggs possess 
the same number of chromosomes as the partheno- 
genetic eggs, plus an equal number which is brought 
in by the spermatozodn. The cleavage nucleus 
exhibits thirty-two chromosomes which may become 
sixty-four in the somatic cells, but unite two by 
two to form sixteen in the odgonia. 
Phylloxera caryecaulis will serve to illustrate 
the chromosome cycle in a species with a life cycle 
composed of parthenogenetic females which alter- 
nate with sexual males and females (Morgan, 1909, 
