614 Gro. W. TANNREUTHER, 
genetic generation where we have the first positive evidence of the 
beginning of a distinct male and female line or the separation of 
sex in the parthenogenetic series. | 
As stated above, the presexual generation, which is produced 
by the fifth parthenogenetic generation, gives rise to either all male ~ 
or all sexual female. In the seven generations that complete the © 
life cycle it is found that sex is distinctly separate in two generations 
only, the presexual (in the sense that male and female, are not 
produced by the same individual) and in the male and female, also 
that the union of sex occurs by fertilization at the beginning of 
the first parthenogenetic generation. Why some of the ova of the 
fifth parthenogenetic generation produce presexual embryos that 
give rise only to males, and other ova produce presexual forms that 
give rise only to sexual females, is a question yet unanswered. 
The early embryonic development of the parthenogenetic and 
sexual generations is very similar, but there are considerable 
differences in the development of the reproductive systems. In the 
developing embryo of the parthenogenetic generation the ovarian 
olands are unspecialized and are often mistaken for primitive ova, 
as shown in Pl. 50, Fig. 43, and the eggs of the following unborn 
generation reach the blastoderm stage before the birth of the embryo. 
On the other hand, in the sexual embryo produced by the presexual 
individuals, the ovarian glands are specialized (Fig. 30), and have 
reached their maximum development, while the ova of the unborn 
sexual developing embryo have not begun to develop at the time 
of birth. 
The winter eggs within the sexual developing individual develop 
very slowly. The time required from the period of ovulation until 
the deposition of the winter eggs is approximately the same as that 
required for the development of a parthenogenetic embryo. This 
verifies the statement that parthenogenesis is a shortened process 
for rapid reproductions and lessens the probable fatality which is 
often due to insect enemies. 
Fertilization of the winter eggs occurs just before deposition, 
but the union of the male and female pronuclei takes place almost 
immediately after the eggs are deposited. As the eggs are being 
deposited they are covered by a thin layer of secretion from the 
accessory glands. At first the secretion is very viscid and has a 
light color, but on being exposed to the air it becomes very elastic 
and forms a thin capsule over the entire egg. The eggs are glued 
