DE GEER. 
55 
snow was at that time on the ground. In some other 
species he found that the number of eggs deposited 
did not number more than twenty, or even less. De 
Geer showed that Leuwenhoek was in error when 
he thought that the apterous females acquired wings 
after having given birth to living young ; and again, 
that after such an acquisition of wings they recom- 
menced the process of viviparition. De Geer, on the 
contrary, showed that the embryos in the pupas are in 
an immature state, and that they do not get their full 
development until the imago has issued and has 
attained its complete growth. With reference to 
puceron de rosier^ ” he continues, *‘I1 est toujours certain 
que les pucerons ailes sont vivipares en tout temps, et 
qu’ils ne pendent jamais d’oeufs.” 
Von Siebold has noticed the curious growth of the 
eggs of one of the small wasps, Nematus ventricosus, 
which affects the gooseberry tree. This growth takes 
place after the eggs are laid, and probably it is caused 
by an absorption of water. Did De Geer contem- 
plate a similar anomaly amongst Aphides when he stated 
his experience that after deposition their eggs do 
not grow to the size of flies’ eggs ” ? 
De Geer’s most important deductions may be thus 
summarised : 
First. That the oviparous forms never produced 
living young. 
Second. That the viviparous female never depo- 
sited eggs. 
Third. That at the end of autumn the viviparous 
females produced those individuals, viz. the males and 
the females, which, through oviposition, provided the 
species for the ensuing year, the egg retaining its 
vitality throughout the rigour of winter. 
Fourth. That if cold weather did not supervene, 
the male and the oviparous females did not occur at 
all. With reference to this head De Geer even thought 
it probable that Aphides living in tropical countries 
might prove to be wholly viviparous. 
