Sex Determination in Phylloxerans and Aphids 285 
means of dispersal for the species at present.* The depositing 
within the gall may be connected with the condition of the gall 
that fails to open soon enough to let the migrant escape. In fact 
the galls do not become well opened until the sexual males and 
females are ready to crawl out. This divergence from the tradi- 
tions of the genus might seem to throw some light on the occur- 
rence of the apterous females of the second generation in P. fallax. 
The late opening of the gall may have led to the depositing of eggs 
within it by some of the winged generation. The presence of wings 
became therefore superfluous, at least except for colonization on 
other plants; hence the opportunity was given for the appearance 
of apterous females that would better insure the continuation of 
the race, since they are not exposed to the great dangers of failure 
to find a suitable plant, ete. Teleological argument of this kind, 
is, | think, of no special value. It is shot through and through by 
the kind of anthropomorphism that exposes much of our zodlogical 
work to reproach. For, to go no further, it is equally manifest 
that the same advantage would accrue to other species even if they 
early opened their galls. 
That the appearance of the apterous forms was due to a sudden 
change—a mutation—is more than probable, since both winged 
and wingless exist at present without intermediates and since the 
wingless condition is obviously an innovation. But the wingless 
individual is not simply a curtailed winged individual—lacking the 
wing-factor, in the latest phraseology—is shown by her egg-laying 
habits. In the winged forms all the eggs ripen at the same time; 
at least they all become fully formed before any are laid. Inthe 
wingless forms, on the contrary, the eggs ripen one (or two) at a 
time in rapid succession and are at once deposited—an apparent 
adaptation since the place of deposit is at hand and taken advan- 
tage of, while the winged forms must retain their egg for deposi- 
tion in a different location. 
A point of unusual biological significance is found in the fate 
of the supernumerary eggs of the stem-mother. She may lay, as 
we have seen, as many as fifty or more; yet the maximum number 
8 In the present case, however, the winged migrants contained only male eggs. This would lead to 
crossing but not to dispersal in any other sense. 
